Laws of Motion

Question 1

What is inertia?

Answer 1

Inertia is the tendency of an object to resist change in motion.

Question 2

How is inertia different from momentum?

Answer 2

Momentum only exists when an object is in motion.

Question 3

In the absence of an external force, a moving object will

Answer 3

move with constant velocity.

Question 4

When the rocket engines on the starship NO-PAIN-NO-GAIN are suddenly turned off, while traveling in empty space, the starship will

Answer 4

Move with a constant speed

Question 5

You are standing in a moving bus, facing forward, and you suddenly fall forward. You can imply from this that the bus’s

Answer 5

velocity decreased.

Question 6

What is the force that stops a soccer ball from continuing forever?

Answer 6

Friction along the ground and gravity through the air.

Question 7

What are the four types of friction?

Answer 7

The four friction types are Sliding, Rolling, Static, and Fluid

Question 8

Why do we need to wear seatbelts in terms of inertia and Newton’s 1st Law of Motion?

Answer 8

If we are in a car we are moving at the same speed. If the car stops suddenly and we are not attached to it (by a seat belt) we will continue to move potentially sending us through the windshield.

Question 9

The equation that is used to solve momentum is p = mv.

What does each of the variables mean?

Answer 9

p = Momentum, m =Mass, v =Velocity

Question 10

What unit of measurement must be used with each variable?

Answer 10

p = kgm/s, m = kg, v = m/s

Question 11

Explain how a golf ball could have more momentum than a bowling ball.

Answer 11

If the golf ball was moving much faster than the bowling ball. Or if the bowling ball was at rest

Question 12

What is the mass (m) of an object with a speed (v) of 10 m/s and a momentum (p) of 5.4 kg-m/s?

Answer 12

5.4=m*10 ⇒ m=5.4/10 ⇒ m=0.54 kg

Question 13

Which has more momentum, a 2000 kg car moving 3 m/s or three 70 kg people sprinting at 8 m/s each?

Answer 13

20003= 6000 or (370)8⇒ 2108⇒ 1680. So the car has more momentum.

Question 14

Conservation of Momentum equation

Answer 14

m1 v initial + m2 v initial= m1 v final + m2 v final

Question 15

A 30 kg child running at 7 m/s jumps onto a 10 kg sled which was initially at rest. What will be the velocity of the child and the sled immediately after the child jumps on the sled?

Answer 15

(3070) +(100) = (30v) +(10v)
210=40v
v=5.25 m/s

Question 16

True or False: Momentum is equal to the mass of an object divided by its velocity.

Answer 16

False

Question 17

True or False: Objects with different masses can’t have the same momentum.

Answer 17

False

Question 18

True or False: Elastic collisions are when two object collide and stick together

Answer 18

False

Question 19

True or False: Momentum can be transferred from one object to another.

Answer 19

True

Question 20

The equation that is used to solve second law problems is F = ma. What does each of the variables mean?

Answer 20

F = Force, m = Mass, a =Acceleration

Question 21

What unit of measurement must be used with each variable?

Answer 21

F = N, m = kg, a = m/s/s or m/s2

Question 22

Use Newton’s second law to predict the effect of an alteration in mass or net force upon the acceleration of an object.

Answer 22

An object is accelerating at a rate of 8 m/s2 when it suddenly has the net force exerted upon decreased by a factor of 2. The new acceleration will be ____4____ m/s2.

Question 23

Use Newton’s second law to predict the effect of an alteration in mass or net force upon the acceleration of an object.

Answer 23

An object is accelerating at a rate of 8 m/s2 when it suddenly has its mass increased by a factor of 2. The new acceleration will be _____16___ m/s2.

Question 24

Use Newton’s second law to predict the effect of an alteration in mass or net force upon the acceleration of an object.

Answer 24

An object is accelerating at a rate of 8 m/s2 when it suddenly has the net force exerted upon increased by a factor of 4 and its mass increased by a factor of 2. The new acceleration will be ____16_____ m/s2.

Question 25

When a 10-kg block is simultaneously pushed eastward with 20 N and westward with 15 N, the acceleration of the block is

Answer 25

.5 m/s2 East

Question 26

A plane has a mass of 30000 kg. The thrust for each of four engines is 15000 N. What is the jet’s acceleration when taking off?

Answer 26

(15000*4)/30000 ⇒ 2 m/s/s

Question 27

What is the difference between mass and weight?

Answer 27

Mass is the amount of matter within an object. Weight is the force of gravity acting on an object

Question 28

What is Newton’s tihrd law?

Answer 28

Newton’s third law says that every ____action_____ force, there is also a __reaction___ force that is __equal___ in size and acts in the _____opposite____ direction.

Question 29

TRUE or FALSE: As you sit in your seat in the physics classroom, the Earth pulls down upon your body with a gravitational force; the reaction force is the chair pushing upwards on your body with an equal magnitude.

Answer 29

False

Question 30

While driving down the road, a firefly strikes the windshield of a bus and makes a quite obvious mess in front of the face of the driver. This is a clear case of Newton’s third law of motion. The firefly hit the bus and the bus hits the firefly. Which of the two forces is greater: the force on the firefly or the force on the bus? Explain.

Answer 30

Newton’s 3rd law states for every action there is an equal and opposite reaction. So if the bus hits the bug then the bug hits the bus with the same amount of force. The bug has a much larger acceleration so there is more damage.

Question 31

Many people are familiar with the fact that a rifle recoils when fired. This recoil is the result of action-reaction force pairs. A gunpowder explosion creates hot gases which expand outward allowing the rifle to push forward on the bullet. Consistent with Newton’s third law of motion, the bullet pushes backwards upon the rifle. Choose one of the options that answer the question and explain your answer. The acceleration of the recoiling rifle is …

Answer 31

smaller than the acceleration of the bullet.

Question 32

What is the difference between contact forces and non-contact forces? Give examples of each.Describe what you must do to find the net force of an object.

Answer 32

Contact forces must touch, like friction, while non-contact do not require this, like gravity

Question 33

Describe what you must do to find the net force of an object.

Answer 33

You must either add/subtract all the forces acting on the object or use the total acceleration and mass

Question 34

Choose a sport or an activity that you love to do. What forces are involved – be specific. When are forces balanced and when are forces unbalanced in your sport or activity?

Answer 34

if there is movement in your activity then the forces are unbalanced and if there is anythin motionless or moving at a constant velcity there are balanced forces

Question 35

Define displacement, distance, speed, instantaneous speed, average speed, velocity and acceleration including units, direction (if applicable) and scalar vs vector quantity.

Answer 35

Displacement= Straight path from start to end - m - vector
Distance= total amount actually traveled - m - scalar
Instantaneous Speed= Speed at a given point in time
average speed = Total distance traveled divided by total time
Speed is distance traveled divided by time - m/s - scalar
Velocity is Displacement divided by time - m/s -vector
Acceleration is a change in velocity over time- m/s/s - vector

Question 36

Calculate the speed for a car that went 125 kilometers in 2 hours’ time. What is the speed in m/s? ( hint: 1000m = 1 km and 1 min = 60 secs)

Answer 36

125 km ⇒ 125000 m
2hrs⇒ 7200 s
125000/7200 = 17.361 m/s

Question 37

If you can walk backward with a speed of 3.5 min/s, how far could you walk in 20 minutes.

Answer 37

d= 3.5(2060) = 4200m

Question 38

Two physics professors challenge each other to a 100. m race across the football field. The loser will grade the winner’s physics labs for one month. Dr. Rice runs the race in 10.40 s. Dr. De La Paz runs the first 25.0 m with an average speed of 10.0 m/s, the next 50.0 m with an average speed of 9.50 m/s, and the last 25.0 m with an average speed of 11.1 m/s. Who gets stuck grading physics labs for the next month?

Answer 38

Rice = 100/10.4 = 9.615 s

la Pas = 25/10 + 50/9.5 +25/11.1 = 2.5+5.263+2.25 = 10. 15 La paz grades

Question 39

George walks to a friend’s house. He walks 750 meters North, then realizes he walked too far. He turns around and walks 250 meters South. The entire walk takes him 13 seconds. What is his velocity?

Answer 39

750 -250 / 13 = 38.46 m/s North

Question 40

You drive a car 150 km from Milwaukee to Chicago in 95 min. What is its velocity in m/s? Were you speeding if the speed limit is 30m/s? (hint need to convert km to meters and min to seconds)

Answer 40

150000/(95*60) =26.31 m/s not speeding

Question 41

The cheetah, which is the fastest land mammal, can accelerate from 0.0 mi/hr to 70.0 mi/hr in . 0.00083 hour. What is the acceleration of the cheetah?

Answer 41

70-0/0.00083 ⇒ 84,337.35 m/s

Question 42

A roller coaster reaches the bottom of a hill with a velocity of 26m/s in 3 seconds. The coaster is accelerating 10m/s2. What is the velocity at the top of the hill?

Answer 42

Vi= Vf-a*t
Vi = 26 - 10*3 ⇒ -4 m/s This does not make sense physically

Question 43

If a speeding train hits the brakes and it takes the train 39 seconds to go from 54.8 m/s to 12 m/s what is the acceleration?

Answer 43

12-54.8/39 ⇒ -1.1 m/s/s

Question 44

How long will it take a car to go from 0 to 44 m/s if they are accelerating at 5 m/s?

Answer 44

44-0/5 ⇒ 8.8 s

Question 45

What does the slope of distance vs time graph represent? What about the slope of velocity vs time graph?

Answer 45

distance vs time slope = velocity

Velocity vs. time slope =acceleration

Question 46

On a distance vs time graph, what is on the x axis and what is on the y axis? Why is it important that the quantity is on the correct axis?

Answer 46

distance on y, time on x. Independent variables should be on the x axis and dependent is on the y

Question 47

What kind of slopes on a distance vs time or speed vs time graphs would show balanced forces? What kind would represent unbalanced forces?

Answer 47

A curved line represents unbalanced forces and both diagonal and horizontal lines represent balanced forces on a distance vs time. On a velocity vs time only horizontal lines are balanced any other type would be unbalanced.