Physics 2

Question 0

Explain what a field is?

Answer 0

an invisible influence capable of exerting a force on a mass or charge.

Question 1

what is gravity?

Answer 1

Gravity is a field that exists between any two objects with mass.

Question 2

what is the equation for gravitational force between two objects with mass?

Answer 2

Fgravity= Gm1m2/r^2

This is often known as the inverse square law

The forces on both masses are equal in size but opposite in direction.

Question 3

whats the difference between gravity and the force of gravity?
How can we derive the value of g from the Force of gravity between two objects equation?

Answer 3

Gravity is the field that is will create a force on a object of mass.

mg= GMearthm/r^2 the m on both side of the equation leaving us with just g=G*Mearth/r^2

F=mg

Question 4

Is the Universal Law of Gravitation true everywhere?

Answer 4

Yes

Question 5

Two planets A and B, where the mass of B is two times that of A. What is the ratio of the forces between them? What is the ratio of acceleration between them?

Answer 5

Well they should have the same forces exerted between them due to Newtons 3rd Law. The acceleration of mass be will be half that of mass A.

Question 6

What force does the earth experience due to a rock falling?

Answer 6

The earth and the rock will experience the same force. The earth will just experience hardly any noticeable acceleration because its mass is so much greater than that of the rock.

Question 7

Important note

Answer 7

F=Gmm/r^2 gives the force due to gravity not gravity itself. Gravity itself, usually called “gravity” or “the strength of the gravitational field” or “acceleration due to gravity” is represented by lowercase g and is described by the formula g=Gm/r^2. Many students mistakenly reference the first formula when asked about gravity.

Question 8

What is the equation for gravitational potential energy? And what is it for liquids?

Answer 8

PE=mgh. Anything with mass can have gravitational potential energy. For example liquids have mass, so they can also have potential energy but we typically replace the mass term with density when dealing with fluids. So PE per unit of volume of fluid= pgh

Question 9

What is the equation we use for potential energy in space or near earth if NOT assuming g=10m/s/s?

Answer 9

PE= -Gmm/r

Question 10

Explain the difference between sliding friction and static friction?

Answer 10

Sliding friction is the force happening between to objects and there surface as it is moving. Static friction is the force when two surfaces are in contact with each other and a force is applied but the object doesn’t move. Think of a box sliding down across a surface and a box you’re trying to push but won’t move.

Question 11

In practice, the acceleration due to gravity is not a constant 9.8 m/s^2, but varies with distance from the center of the earth. Taking this into consideration, as a falling objects approaches the earth what will happen to its acceleration and velocity?

Answer 11

The object will exhibit an increasing rate of velocity change there for and increase in acceleration. Think of gravity equation.

Question 12

What two things are friction dependent upon?

Answer 12

Texture of the two surfaces

The amount of contact force (normal force) involved

Question 13

What does motion does friction always oppose?

Answer 13

It opposes SLIDING, NOT motion

Question 14

Which way does the friction force vector point for a car driving east? For a skidding car with locked breaks? For a gecko climbing a wall? For a car driving around a corner?

Answer 14

Vector will point east, will oppose the sliding of the car, point upwards, inwards towards the center of the circle because the car is trying to slide outward.

Question 15

What are the formulas for kinetic friction and static friction?

Answer 15

Ff= µsFn or Ff=µsmg*cosø

Ff= µkFn or Ff = µkmg*cosø

Question 16

What is the static friction for a box being applied with 20N or force? And 100N of force?

Answer 16

The static friction will oppose the applied force vector but will be equal to it so 20N and 100N

Question 17

500N is applied to an object and it does not move. 501N is applied and it just begins to slide. Describe the amount of force that must be applied to the object continuously to move it at a constant velocity across the surface?

Answer 17

For an object to be traveling at constant velocity the Net force must add up to 0 which will give no acceleration. We know that the normal force and weight force are the same if on a flat surface. So therefore the kinetic friction and the applied force must be the same in order for there to be no accel and remain at constant velocity.

Question 18

Why do objects accelerate down an inclined plane?

Answer 18

Forces are unbalanced because the normal force and the weight of the object aren’t the same due to the incline

Question 19

Explain how you should solve incline plane problems?

Answer 19

First resolve the weight or Force of gravity vector into components. Here you will then get a perpendicular and parallel vector and then solve for these two vectors. The parallel vector will give you force down the inclined plane and the perpendicular vector will give you the normal force. From here you can solve for the net force by adding all the forces acting upon the box.

Question 20

What are the equations used for incline plane problems and what do each do?

Answer 20

F= mgsinø this will give you the component that is parallel to the surface of the incline.

Fn = mgcosø this gives you the force that is perpendicular to the incline which is equal to the normal force because there is no acceleration in either of those directions

Question 21

How do you find the final velocity of an object at the bottom of an incline?
How do you find the acceleration of an object moving down an incline plane?

Answer 21

Use Vf = √(2gh)

Take the net for and divide it by the mass. You can derive the equation a= gsinø because mgsinø = m*a the mass cancel.

Question 22

Why does V = √(2gh) work for either incline or falling body problems?

Answer 22

The formula V = √2gh is derived from conservation of energy by equating mgh to 1/2mv2 and solving for v. As long as friction, air resistance, etc. are ignored, energy will be conserved in an identical way whether the object falls directly to the ground or rolls down a plane.

Question 23

As the angle of an incline increases, what happens to the value of a?

Answer 23

Well we know that a = gsinø so if the angle increases so does sine. (think of your triangle on a graph and what happens to sine as the angle increases). If sine increases therefore a will increase. As the angle increases sine increases cos decreases.

Question 24

What happens to the normal force and the force down the plane as the angle increases for an inclined plane problem?

Answer 24

normal force decreases and force down the plane increases.

Question 25

What are the min and max values for accel down an inclined plane?

Answer 25

Think of your triangle sin of 90 is 1 so that would give 10m/s/s
sin of 0 is just 0 which would give 0 accel.

Question 26

Will a change in mass of a block on an incline cause it to slide down the plane if initially at rest?

Answer 26

No this will just increase the normal force and weight of the block.

Question 27

Tension usually means you are going to be dealing with a force involving?

Answer 27

Rope cable string ect

Question 28

what is the tension of a rope being pulled from opposite ends with identical forces of 50N?

Answer 28

The tension in the rope would be 50N

Question 29

A 500kg elevator is being accelerated upward by a cable with a tension of 6000N. What force does the elevator exert on the cable?

Answer 29

The elevator is 500kg meaning that it weighs 5000 N. If there is 6000 N tension in the cable that means that the 1000 N is going into accelerating the elevator. So the force exerted on the cable iis 6000 N. Newtons 3rd law ??

Question 30

What is hooks law?

Answer 30

F = k∆x springs and many other items such as resilient solids, rubber, and bonds between atoms follow this law.

∆x is the displacement from equilibrium, not length of spring

Question 31

For a mass on a spring when is the velocity the greatest, the least, and acceleration is 0m/s/s

Answer 31

Velocity is greatest when spring is at equilibrium when oscillating, least when its furthest away and velocity is 0, and acceleration is 0 when spring is at equilibrium and even when it passes through equilibrium.

Question 32

A ball rolls along a frictionless table and strikes a spring. Describe the force experienced by the ball due to the spring, the acceleration of the ball, and how both change with time?

Answer 32

As the ball hits the spring and compresses it, the spring then exerts a force in the opposite direction that the spring is compressing. As the spring compress further and further the ball is gaining a greater acceleration vector in the negative direction ( decelerating).

Question 33

How do you solve for the spring constant?

Answer 33

use F=k∆x .. ∆x is the displacement from equilibrium or the difference in displacement between two trials. For F, use the force applied in one trial, or the difference in force between two trials. Remember to convert mass to weight (F=mg).

Question 34

A student hangs a 4kg mass on a spring and it stretches 1m. What is the spring constant and how far will the spring stretch if he attaches a 2kg mass?

Answer 34

First solve for the spring constant using F=k∆x. After that plug in the spring constant and new force in the find out how far the spring will stretch.

Question 35

What is the force of the spring directly proportional to?

Answer 35

The force required to stretch a spring will be directly proportional to the amount stretched

According to Hooke’s law, the force required to stretch the spring will be directly proportional to the amount of stretch.

Question 36

what is the equation for potential energy of a spring?

Answer 36

PE= 1/2 k∆x^2

Although the above formula can be used to solve for all of the variables in the equation, it is more likely to be used in connection with conservation of energy. If a mass with a velocity strikes a spring compressing it, all of its KE will turn into elastic PE. Setting the initial KE to the final PE allows you to predict how far the spring will compress.

Question 37

True or False? A ball moving with twice the kinetic energy can compress a spring twice as far. A ball moving with three times the velocity can compress a spring three times as far.

Answer 37

False.. PE=KE. So KE=1/2kx^2.. If we double KE that will only increase x by √2.

True because 1/2mv^2 = 1/2kx^2 so if v increases by 3 times the left side of the equation equals nine so x will increase by 3.

Question 38

What is a pendulum?

Answer 38

any weight (often called a bob) attached by a rob, string, wire ect. to a fixed overhead point and capable of freely swinging from side to side.

Question 39

For a pendulum when is KE and PE at a max and a min?

Answer 39

PE is at a max at the max height of the bob and a min at the bottom of the pendulums arc. KE is at a max at the bottom of the pendulums arc and at a min at the max height of the bob.

Question 40

When is gravitational PE assumed to be 0 for a pendulum bob?

Answer 40

At the lowest point of its arc. In other words, at the point we assume h=0

Question 41

What value must be low for a pendulum to exhibit SHM? Why does the displacement of a pendulum slowly decrease over time?

Answer 41

The angle of displacement must be small for SHM on a pendulum because we are assuming sinø=ø and we are using this for the restoring force.
Displacement decreases over time due to non conservative forces like air resistance ect.

Question 42

Describe how something can be moving fast but be moving infrequently?

Answer 42

Take the moon for example, the moon travels in orbit at about 10090m/s yet it takes about 27 days for it to complete that orbit and thats infrequent. Frequency is the amount of time it takes an object to complete one cycle.

Question 43

For pendulum problems there are typically two forces acting upon the mass. ( and for incline problems). That is the tension force and the weight force. What force do we resolve into components and why?

Answer 43

We resolve the the weight force into two components because the tension ( normal force for incline) are perpendicular to the motion of the object.

Question 44

For an object in pendulum motion. Why is the tension force greater than the perpendicular component of the Force of gravity? Imagine the two components in your head and what they contribute to.

Answer 44

The perpendicular one is smaller because the mass is moving along a circular path and this is for centripetal acceleration. The mgsinø component is the restoring force that lies tangent to the circular path.
There no need for centripital force at the max height because the mass is paused and not moving. And at the equilibrium position there is no restoring force. Only when the mass is displaced from the equilibrium will there be a restoring force.

Question 45

Does mass have an effect on the period for a pendulum?

Answer 45

No it doesn’t, only will mass on a spring.

Question 46

what is simple harmonic motion?

Answer 46

Anything that oscillates back and forth and can be represented by a sine wave graphically constitutes SHM.

Question 47

what are some examples of SHM?

Answer 47

Mass hanging on a spring and a pendulum

Question 48

What is the formula for the period for a mass on a spring and for a pendulum?

Answer 48

T=2π√(m/k)

T=2π√(L/g)

Question 49

How would you find the frequency for a pendulum or mass on a spring? And what units is frequency in?

Answer 49

just do 1 divided by the period equations, or invert them. The units are Hz Hertz

Question 50

How will increasing the following aspects of mass spring system change the frequency of oscillation? a) mass of object b) length of spring c) mass of spring d) gravity e) the spring constant

Answer 50

If mass is increased of object then frequency will go down. Length of spring wont have any effect. Mass of spring wont have any effect. Gravity wont have any effect. With a stiffer spring ie spring constant higher, then the frequency will be higher.

Question 51

What will decreasing the following in a pendulum system do to its frequency? a) mass of bob b) length of pendulum c) gravity

Answer 51

the mass will have no effect, increasing the length will lower the frequency, lf you increase gravity frequency will go up, think about the restoring force and if gravity is increased the period will be less. mgsinø

Question 52

when all the forces about an object are balanced what does this mean?

Answer 52

Object is in a state of equilibrium

Question 53

what does in mean when an object is balanced?

Answer 53

The net force is 0 which means 0 acceleration Fnet=ma

Question 54

what does static equilibrium mean?

Answer 54

At rest stationary, if you add all forces acting on the object together by the head toe method ect. The resultant vector should equal 0

Question 55

Explain how you would solve for say a sign that is hanging by two strings at different angles attached to a roof?

Answer 55

First, find all the forces acting about the sign, the two tension forces and the weight force. Resolve them into components and solve for both the horizontal and vertical components of each force. Then add up all the horizontal components and vertical components and they should balance each other out and be 0 in the horz and vert

Question 56

For equilibrium problems as the angle with the horizontal increases. say for a sign being held by two wires. What happens to the tension?

Answer 56

Decreases, tension for two ropes holding a sign at 30 degrees will be greater than at 60 degrees

Question 57

Conclusion of Equilibrium

Answer 57

In conclusion, equilibrium is the state of an object in which all the forces acting upon it are balanced. In such cases, the net force is 0 Newton. Knowing the forces acting upon an object, trigonometric functions can be utilized to determine the horizontal and vertical components of each force. If at equilibrium, then all the vertical components must balance and all the horizontal components must balance.

Question 58

Static vs Dynamic Equilibrium?

Answer 58

Static not moving, Dynamic at a constant velocity. Both there is no acceleration.

Question 59

What are some examples when objects are in a state of Equilibrium?

Answer 59

Terminal Velocity, Constant Velocity, Objects are at rest, Balanced fulcrums or boards hanging, Objects floating in liquids

Question 60

How should you solve for equilibrium problems?

Answer 60

Set forces equal to each other: Fleft=Fright Fup=Fdown Tclockwise=Tcounterclockwise. Recommended to make a T on your paper. Right all the forces that would push the object to the right in the right column and all the forces that will push it to the left in the left column. Always draw a free body diagram.

Question 61

A 15kg toy rocket is falling toward earth with a constant velocity of 20m/s. A small amount of fuel still present in the cone creates a downward force of 30 N. What is the force due to air resistance?

Answer 61

The force due to the rockets weight is 150 N and the fuel is also a 30 N force in the downward direction. The rocket is at terminal velocity (no acceleration and in dynamic equilibrium) so the force of air resistance must be equal to the force down ward resulting in 0 net force.

Question 62

What are the formulas for Torque?

Answer 62

T= Fr or T= Frsinø

Question 63

When do you need to use T= Frsinø

Answer 63

You use this when the force applied is not a perpendicular force and is at an angle.

Question 64

How do you solve fulcrum and board on string problems?

Answer 64

These are simple equilibrium problems. Just find the torques exerted on the balanced board or a board attached to a string. Determine if its rotating the board clockwise (-) or counterclockwise (+) and if there is no net torque these will be come out to be 0.. if not there will be a greater torque in one of the directions which will cause an acceleration. DONT FORGET TO FIND TORQUE AND NO JUST THE FORCES

Question 65

Do forces or tension created directly at the rotating position of the board or fulcrum create a torque?

Answer 65

No, this is because the ( r=0). For example a mass right over the center of the fulcrum.

Question 66

If 20 kg hangs exactly 3 meters from the fulcrum, what mass should hang on the other end, 5 meters from the fulcrum, to balance the board?

Answer 66

The 20 kg mass exerts a 200 N force, this means that it exerts a 600 Nm torque. Now all we have to do is set 600 equal to 510m. This would give us a 12kg mass.

Question 67

What does it mean for a system to not be in equilibrium?

Answer 67

This is when an object has an acceleration due to a net force. ( aka translational acceleration problems)

Question 68

How would you solve for the equilibrium of an object on an incline plane?

Answer 68

Use the T method. Call all the forces acting down on the plan “down” forces and all the forces acting up the plan “up forces”. The force down the plane due to gravity is always F=mgsinθ. The force of friction is always parallel to the plane opposite the direction of motion. There will never be acceleration perpendicular to the plane, so you can ignore these forces.

Question 69

A 120kg rocket is accelerating toward the at 8m/s/s. The engine creates a downward force of 200 N. A small parachute is attached to the rocket and slows its decent. What is the force due to air resistance against the parachute. ( assume all air resistance is due to the parachute)

Answer 69

The forces acting down on the rocket are: mg (1200N) + 200N = 1400N. The forces acting up on the rocket are: Fair + ma (120kg*8m/s2) = Fair + 960N. Therefore: Fair + 960 = 1400 and Fair = 440N.

Question 70

For circular motion at constant speed can you derive centripetal acceleration?

Answer 70

Yes

Question 71

For circular motion which way is the change in velocity vector (∆v) pointing?

Answer 71

The change in velocity vector is pointing toward the middle. Think about the khan academy video of how he cut out each tangental velocity vector and put the tails of each vector together and saw how each one changed.

Question 72

So if an object has a constant velocity and is going around in a circle is the velocity changing?

Answer 72

Yes, the magnitude isn’t but the direction of the vector is changing. So this means that there is a net force which is going to cause an acceleration.

Question 73

Just a note

Answer 73

If the velocity of an object is changing in anyway ( magnitude or direction) this means that there is an acceleration taking place meaning that there is a net force acting on the object. This net force is acting in the direction of the acceleration which is causing the change in velocity. This net force is centripetal force.

Question 74

What is the centripetal force, when a yoyo on a string is swung around in a circle? When a satellite orbits the earth? when a car drives around a corner?

Answer 74

The tension in the string, gravity, and the frictional force. These are all pointing inward toward the center of the circle which the object is orbiting around

Question 75

whats the equation for the circumference of a circle?

Answer 75

Circumference= 2π*r

Question 76

if a car is moving at constant speed around a track, is it accelerating?

Answer 76

Yes even though the magnitude of the velocity may not be changing the direction of the velocity vector is changing indicating acceleration. Acceleration is any change in velocity

Question 77

What way is the acceleration vector pointing, for an object traveling around in a circle at constant speed?

Answer 77

The acceleration vector points towards the middle of the circle, the same way as the change in velocity vector (∆v)

Question 78

What is inertia, explain when a car is going around a corner and a person is in it.

Answer 78

Inertia can be described as a resist to accelerate, so when a car is going around a corner at constant speed the person is resisting acceleration and wanting to still move in the same path as the tangent velocity vector. Sometimes as you go around a corner you think your body is accelerating but really its just maintaining the motion of the tangent velocity and resisting a change in acceleration.

Question 79

what is centripetal force?

Answer 79

Centripetal force is the net force ( friction, tension, gravity ect) that causes and object to change in velocity and have an inward acceleration.

Question 80

Centripetal Force

Answer 80

To summarize, an object in uniform circular motion experiences an inward net force. This inward force is sometimes referred to as a centripetal force, where centripetal describes its direction. Without this centripetal force, an object could never alter its direction. The fact that the centripetal force is directed perpendicular to the tangential velocity means that the force can alter the direction of the object’s velocity vector without altering its magnitude.

Question 81

what are the 3 mathematic quantities when analyzing circular motion?

Answer 81

Force, acceleration , speed

Question 82

How do you solve for centripetal force?

Answer 82

Fc=mv^2/r or Fc can be thought of as net force which will always be the centripetal foce.

Question 83

Is centripetal force an actual force?

Answer 83

No, when you see centripetal force think that is always caused by some other responsible force. ( tension, friction, gravitational ect). Centripetal force is just a category name for forces that act to pull things into circular motion.

Question 84

What is centrifugal force?

Answer 84

this forms an action reaction pair with centripetal force. Like when a ball on a string is swung around in a circle. It the string is pulling the ball into the center, the ball must also be pulling on the string ( Newtons 3rd Law). The strings force on the ball is centripetal and the balls force on the string is centrifugal.

Question 85

For a ball in circular motion does the centrifugal force act on the ball or on the string?

Answer 85

the centrifugal force acts on the string. The strings force on the ball is centripetal and the balls force on the string is centrifugal.

The string. In this system a centripetal force upon the ball provided by the string maintains the circular motion, and the reaction to it, usually called the reactive centrifugal force acts upon the string.

Question 86

what is the equation of centripetal acceleration?

Answer 86

ac= v^2/r centripetal acceleration

Question 87

What is the direction of the centripetal acceleration vector?

Answer 87

towards the center, both the centripetal acceleration and centripetal force (ie tension, friction ect) point toward the center.

Question 88

how can a lot of centripetal force questions be solved?

Answer 88

we can just set what force is causing the centripetal force, like for a satellite gravitational force . So mv^2/r=Gmm/r^2 We can do this because that force is the net force on the object which is going to cause the acceleration. Like for a car friction is the centripetal force, and the weight and normal force cancel each other.

Question 89

What force equation should be set equal to the centripetal force in each situation?

Answer 89

• a car going around a corner? µ*Fn = mv^2/r
• a satellite orbiting earth? Gmm/r^2 = mv^2/r
• a ball on a string? Tension= mv^2/r
• a charged particle in a magnetic field? qvßsinø = mv^2/r

Question 90

so what would be the velocity of a satellite orbiting the moon?

Answer 90

Gmm/r^2 = mv^2/r so v= √Gm/r m=mass of earth

Question 91

Derive a formula for the minimum coefficient of static friction between a car and the road to keep a car going around a circular track?

Answer 91

µFn = mv^2/r and the Normal force= mg

so µ = v^2/rg

Question 92

what is the equation for angular velocity? and what are the units?

Answer 92

w = v/r
w = 2πf
rad/sec
v= tangential velocity

Question 93

what is the difference between angular frequency and angular velocity?

Answer 93

You can use these interchangeably for the MCAT. Because angular frequency is just the magnitude of velocity ( scalar)

Question 94

in what direction does the angular velocity ( omega w ) point?

Answer 94

The angular velocity vector points along the axis of rotation. Use the right hand rule to decide if it is up or down. Curl the fingers of your right hand around the axis of rotation such that your fingers point in the direction of rotation and your thumb will be pointing in the direction of the vector.

Question 95

how in many cases, can we solve angular momentum problems linearly?

Answer 95

Take the circumference of the circle as a translational distance:

C= 2πr or C=πd and use this distance just like you would along a straight path.

Question 96

A ball with a radius of 11cm is spinning at a rate of 24 rad/s. How far does the particle on the equator of the ball travel?

Answer 96

We know that there are 6 radians for every 1 revolution. Therefore in 1 second we know that the ball spins 4 times. So now we can find the circumference of the ball and multiply this by 4 which will give us the distance. C= πd C= about 66 cm 664= 264 cm

Question 97

If you see something in radians how do you convert it to degrees and vice versa

Answer 97

use the conversion factor π/180

Question 98

How do you know if an object is in rotational equilibrium?

Answer 98

If it is NOT rotating… or it is rotating with a constant angular velocity

Question 99

When a sports team is on the move and is going to take some effort to stop?

Answer 99

The sports team has the momentum

Question 100

All objects have mass, so if an object is in motion then it has what?

Answer 100

Momentum

Question 101

What is momentum dependent upon?

Answer 101

The amount of mass of the object and how fast it’s traveling

Question 102

Momentum is a vector. There was be a direction in which way the object has the momentum in.

Answer 102

Just a note

Question 103

The more momentum an object has the harder it is going to be to stop which means?

Answer 103

There is going to have to be a force involved. And the larger the momentum the larger the amount if force it is going to take or longer period of time or both in order to bring the object to a hault. We have witnessed this in our cars. When we come to a stop the brakes apply a force for a given amount of time to bring the car to a stop. The more momentum the larger the force its going to take or will take a longer amount of time.

Question 104

What is always the causing factor of accelerating an object?

Answer 104

An unbalanced force. Either speed up the object or slow it down. which in turn increases or decreases the momentum.

Question 105

what does impulse equal?

Answer 105

The change in momentum

Question 106

Say a half back experienced a force of 800N for 0.9 seconds. What would be the impulse?

Answer 106

The impulse is 800 * 0.9. This is also equal to the half backs change in momentum

Question 107

Just a note.

Answer 107

Observe that each of the collisions above involve the rebound of a ball off a wall. Observe that the greater the rebound effect, the greater the acceleration, momentum change, and impulse. When a ball is rebounded off a wall if is initial velocity is 25 m/s and it comes of at 20 m/s that has a greater v change a change momentum change and impulse than something that is 10 m/s to 5 m/s. You have 25 and -20 vs 10 and -5.

Question 108

Just a note

Answer 108

In a collision, an object experiences a force for a given amount of time ( impulse) that results in its mass undergoing a change in velocity (i.e., that results in a momentum change).

Impulse=change in momentum

Question 109

Describe why we use air bags in cars?

Answer 109

When the driver gets in a wreck he will continue to move will his momentum. Since change of momentum is = to impulse. The longer it takes for the driver to come to a stop the less force has been exerted on the driver. This is because F*t are inversely related and = to the change in momentum

Question 110

explain situations of rebound?

Answer 110

when something rebounds it undergoes a big velocity change compared to something that say just hits a wall and stops. This is because the direction of the velocity is also changing. Will a big velocity change this also means that there was a big change in momentum which means that there was a large impulse.

Question 111

Explain how momentum is conserved?

Answer 111

Think about it, say a car runs into a car that is stationary. The second car will experience a force from the first car, and the first car will experience the same force in the opposite direction ( 3rd law ). So we have Ft= -Ft and this is equal to impulse which is equal to change in momentum.

Question 112

In a system what is the only way momentum change?

Answer 112

Momentum can only change if there is a net force acting on the system (basically reacts with its souroundings) . Because net force= ∆p/∆t

Question 113

What is the equation for momentum?

Answer 113

p=mv

Question 114

What should we think of momentum as?

Answer 114

Momentum= inertia increased by velocity

Question 115

is momentum always conserved in a ISOLATED system?

Answer 115

yes. you will see this most in collision problems (including reverse collision). Isolated means that there are no external forces acting on the system. Friction and drag are common external forces.

Question 116

what are the units of momentum?

Answer 116

kg*m/s

Question 117

A 10kg block falls from a height of 10m onto a table that is 5m high. Was momentum conserved during the fall? Was momentum conserved during the collision with the table?

Answer 117

If you define the ball as your system, then gravity is an external force so momentum will not be conserved. However, if you defined your system to include the earth and the ball then momentum would be conserved. At rest the ball had no momentum and whatever momentum it gains as it increases in velocity will be matched by an increase in momentum of the earth. Because they will be vectors in opposite directions they will cancel to zero and momentum will have been conserved: zero before, zero after. In the collision with the table, momentum will be conserved for the ball-table-earth system, but not the ball-table system. All of this, of course, assumes no external forces.

Question 118

What is the definition of impulse?

Answer 118

Impulse is the change in an objects momentum.

Question 119

what is impulse equal to?

Answer 119

=∆p
=m∆v
=Favg*t

Question 120

If there is no change in velocity can there be an impulse?

Answer 120

No,

however, the greater the change in velocity, the greater the impulse (assuming constant mass)

Question 121

How is impulse= m∆v the same as impulse= Favg*t

Answer 121

We know that F=ma which is the same as F=m∆v/t. So if we multiply t over, we get Ft=m*∆v and this gives us impulse is equal to momentum.

Question 122

Car collision problems are frequently used to test your understanding of impulse.
-Air bags increase the time during which the driver comes to rest during a collision. How or why would this prevent injury?

Answer 122

The driver is going to have some momentum when it comes in contact with whatever is causing the collision. So when this happens the driver is going to have some velocity and (mass) this means that he has momentum. F•t = m∆v so by increasing the time it takes for him to come to a stop there will be less force acting upon him. F•t are inversely related

Question 123

A 1kg rubber ball falls from some heigh, and strikes the cement at a final velocity of 10m/s. If the ball experiences a completely elastic collision, what will be the velocity of the ball after the collision and the impulse experienced by the ball, respectively?

Answer 123

10m/s and 20kg*m/s

Question 124

what is the difference between elastic and inelastic collisions? what is conserved and what is not

Answer 124

in an elastic collision momentum and kinetic energy is conserved.
in a inelastic collision momentum is conserved but NOT kinetic.

Question 125

If an object is deformed during a collision it must have undergone what type of collision?

Answer 125

inelastic, when an object undergoes deformation this means that you are loosing energy and in elastic collisions no energy is lost.

Question 126

what equation should we use for elastic collisions?

Answer 126

Just use conservation of energy equation because no energy is lost in elastic collisions 1/2mv^2+1/2mv^2 = 1/2mv^2 + 1/2mv^2

Question 127

Conservation of relative speed

Answer 127

For completely elastic collisions ONLY, the relative speed before will equal the relative speed after.

Question 128

why must the collision be elastic for conservation of relative speed?

Answer 128

Because in order to for the relative speed to be conserved there must be conservation of energy.

Question 129

Objects exchange velocities: If the objects of equal mass and the collision is perfectly elastic, the two objects will exchange velocities before and after the collision. Why? Describe conceptually why/how the objects exchange their initial velocities?

Answer 129

For a head-on collision with a stationary object of equal mass, the projectile will come to rest and the target will move off with equal velocity, like a head-on shot with the cue ball on a pool table. This may be generalized to say that for a head-on elastic collision of equal masses, the velocities will always exchange. mv=mv

Question 130

For inelastic collisions what equation should we use?

Answer 130

Use the conservation of momentum. You MUST USE SIGNS. any velocity vectors left or down must be given a negative sign.
mv+mv = mv+mv and this equation becomes mv+mv = (m + m)v this is because the objects stick together.

Question 131

What is a reverse collision?

Provide at least 3 examples?

Answer 131

• This is when two objects are together and they come apart.
• A bomb. Two ice skaters pushing off each other. Radio active decay

Question 132

Swuppose an atom of 56Fe undergoes alpha decay. The velocity of the exiting alpha particle is 2.0*10^3 m/s. What is the identity and ejection velocity of the decay product?

Answer 132

The new particle formed has 52amu (Cr-52). This can be determined by subtracting the A and Z number for Helium from Fe-56. The momentum of the ejected particle must equal the momentum of the decay product, therefore: (2 x 103 m/s)(4 amu) = (v)(52 amu). This simplifies to 8 x 103/5.2 x 101 = 154 m/s.

Question 133

What is the formula for stress?

Answer 133

Stress = Force/Area

Question 134

What is the formula for Strain?

Answer 134

Strain = ∆dimension/ original dimension

Question 135

What is the formula for moduli of elasticity?

Answer 135

ME = stress/strain

Question 136

What is Young’s modulus?

Answer 136

Youngs Modulus = tensile or compressive stress/strain modulus (simultaneous pushing or pulling forces on both sides of an object; the two forces must be exactly aligned in both vertical or horizontal planes)

Question 137

What is Shear Modulus?

Answer 137

shear stress/strain modulus ( simultaneous pushing or pulling forces; tow forces are NOT aligned)

Question 138

What is Bulk Modulus?

Answer 138

Bulk Modulus = bulk stress/strain modulus (simultaneous compression from all sides)

Question 139

Which object has the highest ME a marsh mellow or a rock?

Answer 139

The higher the Modulus Elasticity the better the object is able to keep its shape. So the rock would have the higher ME

Question 140

What happens when solids are heated or cooled?

Answer 140

When heated they expand, when cooled they shrink

Question 141

What is the equation for thermal expansion?

Answer 141

∆L = alphaL*∆T

Question 142

Why is water weird?

Answer 142

Water exhibits some notable exceptions to the thermal expansion rules above. As long as water remains a liquid, it follows trends we would expect, with volume increasing as temperature rises and decreasing as temperature falls.

However, once water gets very near to its freezing point, ice crystals begin to form and it actually begins expanding.
This is due to the highly ordered lattice structure of the solid (ice), which includes regularly alternating hydrogen bonds.

Water is one of very few substances for which the solid phase will float in the liquid phase.

Question 143

Several ice cubes are added to a drinking glass. Water is then added until the glass is just on the verge of overflowing. All of the ice cubes are floating at the top of the water. When viewed from the side, it can be seen that the ice cubes are sticking up out of the water and above the rim of the glass. If the glass is left to equilibrate to room temperature will the glass overflow?

Will the water level be higher or lower once all of the ice cubes have melted?

Answer 143

?

Question 144

what is energy?

Answer 144

Energy = the capacity to do work

Question 145

whats the equation for KE?

Answer 145

KE = 1/2mv^2

Question 146

What is the equation for PEgravitational?

Answer 146

PEgrav = mgh (near earth)

PEgrav = -Gmm/r (away from earth)

Question 147

What is equation for PEelastic?

Answer 147

PEelastic= 1/2k∆x^2

Question 148

What is the equation for PEelectrical?

Answer 148

PEelectrical=qv

Question 149

What is the equation PEcapacitor?

Answer 149

PEcapacitor = 1/2QV or 1/2CV2 or 1/2Q2/C

Question 150

What is internal energy?

Answer 150

The energy of the internal vibrations and random motions of molecules and/or atoms within a system. Non conservative forces such as friction or drag acting on a moving object results in the transfer of kinetic energy into internal energy.

Question 151

What is heat energy?

Answer 151

Energy dissipated as heat. On the MCAT this is usually heat dissipated from a collision, or from a current-carrying wire. The terms heat energy and internal energy are used almost interchangeably.

Question 152

What is chemical energy?

Answer 152

The energy contained within chemical bonds, or the energy stored/released due to the separation and/or flow of electrons. ( ie a battery)

Question 153

What is mechanical energy?

Answer 153

It is the total of KE+PE = ME

Question 154

In the absence of non conservative forces ( friction , drag ect) is mechanical energy always conserved?

Answer 154

Yes, mechanical energy the total energy

Question 155

Name the type of energy possessed or created by each of the following? 1) an explosion 2) a chemical reaction 3) a collision 4) any moving object 5) any object with height 6) a spring 7) a battery 8) two positive charges 9) water in a tank

Answer 155

Name the type of energy possessed or created by each of the following:
• An explosion = Chemical energy turns into heat energy and the kinetic energy of any flying debris;
• A chemical reaction = In a chemical reaction chemical energy is transferred between reactants and products—in an exothermic reaction heat is released
• A collision = in a collision the KE of the objects before the collision is transferred into heat energy used to create damage/deformity/etc.
• Any moving object = any moving object has kinetic energy
• Any object with height = potential energy, any object with height has gravitational potential energy
• A spring = mechanical energy, elastic potential energy, a spring stores elastic potential energy
• A battery = chemical energy, a battery stores chemical energy
• Two positive charges = electrical potential energy, two separated charges contain electrical potential energy
• Water in a tank = potential energy, water in a tank has gravitational potential energy and kinetic energy of the molecules

Question 156

Describe the energy transformations that take place as a rocket ignites and combusts its rocket fuel, launches into the air, rises to a max height, then falls back to earth and strikes the ground..

Answer 156

48. Chemical energy stored in the bonds of the rocket fuel is transferred into kinetic and gravitational potential energy as the rocket rises. If air resistance is taken into account some energy will also be dissipated as heat due to drag. Gravitational PE reaches a max at the max height and is then transferred back into kinetic energy (and heat if considering air resistance) as the rocket falls back to earth. When the rocket strikes the ground its kinetic energy is transferred into heat energy.

Question 157

What is the law of conservation of energy?

Answer 157

Energy is an ISOLATED system is always conserved. Energy is frequently transferred back and forth between forms, but never lost.

Question 158

Provide conceptual definitions for open, closed and isolated systems?

Answer 158

Open System = both mass and energy can be exchanged with the surroundings; Closed System = energy, but not mass, can be exchanged. Isolated System = neither mass nor energy can be exchanged.

Question 159

In order for a force to be qualify as have done work on an object…?

Answer 159

There must be a displacement and the force must have caused this.

Question 160

for the work equation. there is cosø. how do you determine the angle?

Answer 160

the angle is the angle between the displacement vector and force vector.

Question 161

what does work equal?

Answer 161

W=∆Energy
Think of work this way first! Be on the look out for any changes to the total energy of an object or system- IF ENERGY CHANGED, THINK WORK! Most students tend not to recognize or think about work when it appears on the MCAT.

Question 162

When there is a change in velocity has work been done?

Answer 162

Yes, this means a change in KE. ( this is the most common example of how the MCAT might trick ya)

Question 163

Changing in height has work been done?

Answer 163

Yes, this is a change in PEgrav which means a change in energy which means work.

Question 164

is work done when there are changes in masses/planets/ect in space?

Answer 164

Yes, this is a change in PEgrav which = work

Question 165

Change in position of charge means work?

Answer 165

yes this is a change in electrical PE which would be equal to the work done.

Question 166

compression of a spring has work been done?

Answer 166

yes there has been a change in elastic potential energy which would equal work.

Question 167

change in Friction or air resistance what should you think of?

Answer 167

Work, work=∆E

Question 168

What is the equation of work?

Answer 168

W= Fdcosø think of work this way second

Any time a force is applied across a displacement, work has been done. Students ten to think of this only as something like pushing a block across a table. Howeber, if a ball falls from a height, a force (mg) has been applied across a displacement . All of the examples of energy change listed above fir within the formula above

Question 169

What is the units of work?

Answer 169

Joules. But this can be broken down into kg*m^2/s^2. This comes from F=ma

Question 170

When is work positive? when is work negative?

Answer 170

There are two conventions for the sign of work. In physics, we say that if the force and the displacement are in the same direction, work is positive (e.g., pushing a barbell up). If force and displacement are in opposite directions we say work is negative (e.g., lowering a barbell). In both physics and chemistry a common convention is used that says: If work is done on the system it is positive; if it is done by the system it is negative.

Question 171

what does the 1st law of thermo and what is the equation?

Answer 171

energy change is not always completely due to work; some energy is often lost to heat. Work and heat are the only ways energy can be transferred in and out of a system. The 1st Law of Thermodynamics
Work = energy transfer via a force
Heat = energy transfer via friction or energy flow from hot to cold
ΔE=W+q

Question 172

What is the Work-Energy Theorem?

Answer 172

If a net force does work on a rigid object, the work done on that object is equal to the change in the KE of the object.

W = KEfinal - KEinitial

Focus on ∆E though because this means the same thing just will other types of energy as well.

Question 173

Describe the work done when a force, applied at an angle of 45 degrees to the horizontal, is used to push a box across the floor. Describe the work done when a box is moved at a constant velocity across a frictionless table. Describe the work done by the string when a ball on a sting is swung in a circular motion.

Answer 173

When the force is not in the same direction as the displacement, only that component of the force that is aligned with the displacement does work. Thus the work done is Fdcos(45degrees). If the angle between force and displacement vectors is 90 degrees then no work can be done by that force. If a box is moved at constant velocity horizontally no work is done because there was no net force and the energy of the box was the same before and after the motion (ignoring some net force necessary to get the box moving). For a ball on a string no work is done by the centripetal force created by the string because this force is exactly 90 degrees to the tangential displacement vector at any instant.

Question 174

how much work is done when a 1000kg car traveling at 40 m/s applies its brakes and comes to a stop?

Answer 174

just plug in and find kinetic energy. Should be 0 - 800,000 J =
-800,000

Question 175

what is the work done on a spring compressed by 0.5 meters?

k=10 N/m

Answer 175

use PE= 1/2k∆x^2 and W= ∆E 0-1.25= -1.25 Nm

Question 176

can a simple machine out put more force than was put into it?

Answer 176

No, it follows the conservation of energy

Question 177

what are machines?

Answer 177

machines are things that reduce the amount of force necessary to perform a given amount of work

Question 178

Does a machine ever reduce or change the amount of work?

Answer 178

No machines NEVER reduce or change the amount of work

Question 179

what is helpful thing to do when working a machine problem?

Answer 179

Sometimes its useful to first find the force needed to lift or move an object without a machine. With that you then can compare that to the force necessary with the machine. These values will differ by an exact ratio. ( h/d, L1/L2 ect)

Question 180

What is the equation to find the force necessary to lift a mass without a machine?

Answer 180

Fnecessary = mg

Question 181

Whats the equation that give force necessary to do work with a ramp type of machine?

Answer 181

Fm= mg(h/d) h is the height of the ramp and d is the distance of the hypotenuse. This force needed to do work will be less than without the machine. But remember you still do the same amount of work with or without the machine. When MCAT says a ramp is 5m long this means that hyp is 5m

Question 182

A worker must move a 50kg block onto a table that is 2m off the floor. How much work will be required without the use of a machine? If a worker constructs a ramp that is 2m high and 8m long, how much force will be required? How much work will be required with the use of the machine?

Answer 182

-1000 J of work will be required with and without the machine. 125 N of force with using the machine

Question 183

what is the equation for the force necessary when dealing with a lever? Remember work will still be the same amount of force required is the only thing that will decrese

Answer 183

Fm = mg(L1/L2) where L1 and L2 refer to the lever arms for the mass and the applied force, respectively.

Question 184

what is the equation for the force necessary for pullys to do a certain amount of work with the machine?

Answer 184

Fm = mg(# of vertical ropes directly lifting the mass)

CAUTION not every rope that is vertically oriented should be counted and entered into the above equation. To be counted, a vertical section of rope must lift the mass directly, either by being attached to the mass, or by lifting a pulley that is attached to the mass. To test this, imagine grabbing only that rope and tugging it upward. Would it lift the mass?

Question 185

whats the equation for the force required to do a amount of work with a machine using a hydraulic?

Answer 185

Fm= mg(h1/h2) or F=mg(A1/A2) where h1 and h2 refer to the distance traveled by the large plunger and the small plunger, respectively; and A1 and A2 refer to the cross sectional areas of the small plunger and the large plunger, respectively

Question 186

Draw schematic plans for a ramp, lever, pulley and hydraulic lift that each provide a mechanical advantage of 5. Show these to your tutor and check if they are viable.

Answer 186

?

Question 187

how can power be defined?

Answer 187

The rate of doing work or the rate of using energy. These are equivalent because one unit of energy must be required to do 1 unit of work

Question 188

Describe what power is?

Answer 188

The quantity that has to do with a rate which a certain amount of work is done.

Work has to do with a force causing a displacement but it has nothing to do with the amount of time this force acts to cause the displacement.

Question 189

if someone or something does the same amount of work in less time. Like a 2 weight lifters shoulder press the same amount of weight but one does it in less amount of time. Who is more powerful?

Answer 189

The weight lifter that does the same amount of work in less time does more work.

Question 190

what is the unit of power?

Answer 190

Power is in Watts which is also = Joules/s

Question 191

When you first see power what should you think of? (what is power=to?)

Answer 191

P = ∆E/t and this the same as P = W/t because W=∆E also

P = Fdcosø/t because W= Fdcosø

Question 192

when you see instantaneous power what equation should you use?

Answer 192

P= Fvcosø this is only used for instantaneous power!

Question 193

Truck engine A has twice the power of truck engine B.
True or False?
a) Truck A can accelerate the same trailer from zero to 50m/s in half the time

b) Truck A can accelerate a trailer to a velocity v, in a time t, that is twice as massive as the trailer truck B can accelerate to the same velocity in the same time period.
c) Truck A can accelerate the same trailer to twice the velocity in the same amount of time.

Answer 193

True if you break down the equation where W= ma*dcosø you can see the acceleration will double if the power has doubled.

True just as above this question is regarding mass

Question 194

How are work energy and power all related?

Answer 194

Work- refers to an activity involving a force and movement in the directon of the force. A force of 20 newtons pushing an object 5 meters in the direction of the force does 100 joules of work.

Energy- is the capacity for doing work. You must have energy to accomplish work - it is like the “currency” for performing work. To do 100 joules of work, you must expend 100 joules of energy.

Power-is the rate of doing work or the rate of using energy, which are numerically the same. If you do 100 joules of work in one second (using 100 joules of energy), the power is 100 watts.

Question 195

what equation is used for the force of gravity between two objects?

Answer 195

F=Gmm/r^2

Question 196

when an object is hung from a spring and then you put a heavier object on the spring how would you find the spring constant?

Answer 196

take the difference of the forces and the difference of the lengths stretched and then use these values for ∆x and F. You can only find the spring constant if the same spring is used for both masses.

Question 197

How would you find the instantaneous velocity of something in orbit?

Answer 197

When an object is in circular motion even though it may be at constant magnitude of velocity, the direction of the velocity vector is changing. So this indicates that there is an acceleration which means there is a net force. Centripetal acceleration to be exact, is caused by some force pointing inward toward the middle of the circular path. this is Centripetal Force. So we know that this Force tension gravity ect is equal to the Centripetal force so we can set lets say Gmm/r^2 = mv^2/r and then solve for v

Question 198

If something is pressed against a spring. When does that object have the greatest force on it. When this object rebounds from the spring when is acceleration greatest?

Answer 198

When something hits a spring the force is greatest when the spring is fully compressed. The acceleration of the object is greatest right when you let go of the spring because the force is greatest at that point a= F/m .

Question 199

what way is the friction vector point for a car driving east why?

Answer 199

Its pointing to the east because this vector opposes the sliding of the tire.

Question 200

if an object is going 40 m/s and friction accelerates it (decelerate) at a rate of 4m/s/s. how far does the sled go?

Answer 200

v=d/t so the sled will take 10s to stop. Then we find the average velocity of 20m/s and then multiply to get 200m.

Question 201

if you have a net force ( say for instance centripetal force) of something how can you solve for the instantaneous velocity?

Answer 201

well when an object is in circular motion we know that there is a net force acting toward the center (centripetal foce). which is just the force of gravity. So we can set mv^2/r= Gmm/r^2

Question 202

if a rock is falling downward at an acceleration of 8m/s/s. What is the net force due to air resistance? mass of 10kg

Answer 202

Draw a free body. We know that there is a weight force point straight down at 100 N. We know if an object is accelerating there has to be a net force involved and here the net force will be in the downward direction because thats the way the object is accelerating. So add ma to the loosing side which is the Fup side and then solve 100 = Fup + (10)(8) 20N

Question 203

If an object is accelerating upward what way is the net force pointing?

Answer 203

There is a net force in the upward direction. so an 1000 kg elevator being accelerated upward at 2m/s/s find the tension in the rope. 10000 + ma = Fup 12000

Question 204

If an object say on a fulcrum is perfectly balanced. Is there a net toque on the object?

Answer 204

No, there is no net torque on the object it is in equalibrium. If there were a net torque the object would accelerate some amount in the clockwise or counterclockwise direction.

Question 205

if a mass is attached to one end of a board with a fulcrum under it. what mass would have to be attatched to the other end to balance it.?

Answer 205

all you do in a question like this is set the TORQUES equal to each other and solve Tclockwise=Tcounterclockwise T=Fdsineø

Question 206

when you see average force on the mcat what is this a dead giveaway of what you’ll be dealing with?

Answer 206

This is a dead giveaway that you’ll be dealing with Work or Impulse. Remember the ∆E is equal to the amount of work. So if someone has a KE of 120 and then gets stopped. How much work was done? 120 then we can just divide this by the distance traveled and it will give us average force.

Question 207

if there are two objects and one of them as 2 times as much power of the other. the first can pull a trailer with twice the weight in the same amount of time up a hill? Do twice the work in the same amount of time? Accelerate a trailer from rest with the same weight to twice the speed in the same amount of time?

Answer 207

True, True, False.

When solving questions dealing with power. Think about what power equals (∆E, and works over time) So its the amount of work done over a period of time. Two people can do the same amount of work but one may do it twice as fast meaning double the power. Also think about energy like KE=1/2mv^2 and how much power it would take to double the speed. It would take 4 times as much power.

Question 208

for what type of collision do you have to worry about the signs?

Answer 208

inelastic conservation of momentum you have to keep track of signs but conservation of energy you dont. thats why for elastic collisions we use KE+KE=KE+KE

Question 209

for pully problems what has the exceed number of ropes be pulled either by the box or by a person (2). The number of vertical ropes directly lifting the mass.

Answer 209

Note.

Question 210

For any question that machine question that asks how long the ramp must be or how long the board is on the fulcrum ect. Or to figure out how much a person could lift using the aid of a machine what should you do?

Answer 210

First find how much the object would take to lift without the machine or how much the person can lift without the machine.

In this case, the crate requires 1,000 N of force, but the worker is only capable of 200 N. So he must magnify the distance by a factor of 5 to keep the work the same. A machine doesn’t change the amount of work done ever.

Question 211

when are velocities exchanged in an elastic collision?

Answer 211

When the masses are the same

Question 212

When is ME the highest for an object? what is the equation for stress?

Answer 212

When it doesn’t distort or strain as much under a given stress.

stress = Force/area

Question 213

rotational equilibrium vs translational equilibrium

Answer 213

external forces must sum to 0, with rotational external torques must sum to 0

Question 214

conservation of momentum and energy

Answer 214

Remember that momentum is ALWAYS conserved in a collision! Whether it is angular or linear momentum, elastic or inelastic collision, momentum is always conserved! This makes A and B clearly false because the stem asks for entities that are NOT conserved. Mechanical energy is the sum of potential and kinetic energy. The wrench had potential energy when it was dropped, but we are told by the stem to focus only on the collision itself. At the moment the collision occurs the wrench has no potential energy. Immediately after the collision it will have no potential energy either, and so it can be said that potential energy was conserved, or “remained constant” across the collision. These observations combined make C the correct answer. KE is conserved only in perfectly elastic collisions. One of the hallmarks of a perfectly elastic collision is no deformity or damage to the two objects. It is almost certain the wrench and/or the turbine blade will be scuffed, scratched, bent or broken in some way as a result of the collision.