Kinematics and Newton's Laws Flashcards
What is the density of water?
1000 kg/m3 or 1g/cm3
What is elementary electric charge?
1.6 E^-19
What is Coulomb’s constant?
9 E^9 (Nm^2/c^2)
What is plank’s constant?
6.626e^-34
What is speed of light in a vacuum?
3 E^8
What is a proportion?
Relationship between 2 or more variables
ex) What happens to the area of a circle if the radius doubles?
A=Pi r^2
If radius doubles, that means area is quadrupled (yay)
What are the steps to solving proportion problems?
1) determine equation that relates the two variables
2) identify the constant component in equation
3) Write the equation as a proportion without constant
4) Plug in factor by which the independent variable is changing
5) Solve for the factor by which the variable of interest is changing
What are the 4 SI units for length, mass, time, and charge
m, kg, s, C
What are variables for speed?
m/s
What are the variables for density?
kg/m3
What are the variables for work?
kg(m^2)/ (s^2)
What is the multiple of a pico?
10^-12
What is the multiple of micro?
10^-6
What is the multiple of milli?
10^-3
What is the multiple of centi?
10^-2
What is the multiple of mega?
10^6
What is the multiple of giga?
10^9
Which formula could give speed v, with which the sound travels through a medium whose bulk modulus is B (kg/ms^2) and whose mass density is p (kg/m^3)?
Try to make your formula into m/s
So this means that (b/p)^.5 can give this
What is distance? is it scalar or vector?
Distance is scalar , it means length of path, units are meters
What is displacement, is it vector and scalar?
It is a vector, and is independent of path taken.
A runner runs around a circular track with radius of 100. m. What is displacement, what is distance?
Diaplacement: 0
Distance: 200 pi
What is speed?
How fast is something going? Average speed= (distance/time) Scalar V V=m/s
What is the velocity?
Speed+ direction
If one lap takes 2 mins, what is speed, what is velocity (same track as last example) ?
Speed = d/t =(200pi/120)= Velocity= displacement/time= 0
What is instantaneous velocity?
speed and direction at a certain point.
What is acceleration?
change in velocity / change in time
change in velocity = V final -V initial
What are units for velocity?
m/s
How do you subtract vector arrows?
You flip the V0 arrow to it’s opposite configuration
How to you connect arrows?
you do the tail to tip method
Suppose a car is travelog to the right, where is the velocity vector facing?
the right
In the same car scenario, where is the acceleration vector going if you press on gas?
To the right
How about when you press on brakes (acceleration) ?
To the left, to the left
How about if your car is going around a turn at constant speed?
Your velocity changes direction.
What are two different ways you can change velocity?
the magnitude or direction
What does uniformly accelerated motion mean?
It means that the acceleration is constant
Name the big 5 equation:
1) d=0.5(Vo-V) t
distance= average velocity over time times time
2) V=Vo+at
how quickly you are moving now = the velocity you started with + acceleration(time you have been traveling)
3) d=Vo(time) +0.5(at^2)
distance can be calculated (usually this is for downwards cliff problems) by seeing how long something takes to fall down
4) d=vt-0.5(at^2)
5) V^2=Vo^2 + 2ad
How do you know which of the big 5 to use for problems?
1) look for variables
2) look for what you need’
3) decide which equation
Example: A particle with initial velocity of 4 m/s, final velocity if 14 m/s, in the span of 3 seconds?
What is the distance that this particle had travelled?
You use the first equation:
d=0.5(4+14)(3)
d= 0.5(18)(3)=27 m
ex) A particle starts at rest and then and travels under constant acceleration.
If the particle travels a distance of d in T seconds, at what time will the particle travel a distance of 2d?
Acceleration is constant, so Big 5 equation can be used.
the particle speed is d/t. At what time will it travel 2d?
We know distance, initial velocity
We need to know time.
Use the 3rd equation.
d=t^2 after taking out constants
So, now that we know that if you want 2d, you would need to have (2)^.5 t.
Don’t assume variables unless they are explicitly given or their value is mentioned.
Example:
An object is thrown straight upwards with an initial speed of 8m/s
It took 3 seconds for the object to strike the ground. From what height was the object thrown?
We know initial velocity (8m/s)
We know final velocity (0 m/s)
t=3
a=-10m/s2 (gravity vector is downwards and neg. if you take your positive to be upwards)
Which of the big 5 equations can we use?
You can use equation 3.
d=(8)(3)+.5(-10)(3^2)
d=-21m
Refer to it as displacement rather than distance, as you are using velocity to solve this problem.
What are the 3 points you can get with a graph (WITH Y AXIS AS VELOCITY AND X AXIS AS TIME)
1) value at a point
2) slope (acceleration)
3) Area under curve (displacement)
What are ways that can imply values of kinematic variables without stating them directly?
Dropped: Vo=0
a=g
Starts from rest: Vo=0
Stops: v=0
Moving at constant speed: a=0
If you throw a ball into the air, when does the force of your throw stop acting on the ball?
At the peak? There is no clear intuition, so we rely on Newton’s laws.
What is Law of Inertia?
Velocity of an object tends to remain constant unless if there is an applied net force
What is mass?
measure of an object’s resistance to change.
Kg
What is Net force?
Vector sum of all forces.
What does a net force produce?
It produces a net acceleration if it is applied.
Mass is a positive scalar,
so F net and A point in the same direction
F(net)=m(a)
What are the forced at play on a person going upwards in an elevator?
What are the forces require to accelerate a 50kg person upwards at a rate 2m/s^2 in a 1000 kg elevator car suspended by a cable?
The forces involved are:
1) downwards gravitational force/weight (is experienced with mass in a gravitational field/Weight=mass times gravity))
2) Rope force/Tension (applied when you have a taught rope/chain, is a pulling force)
3) upwards F normal (force exerted by a surface to keep itself intact, 2 surfaces being pressed together)
All forces except electromagnetic force and gravity function only when surfaces are in contact with each there.
So tension force does not act on the person, but normal force does.
Fnet=MA
F (normal)-W=ma
F(normal)-mg=ma
Fn=m(g+a)
Fn= 50kilo(10+2)=600 newtons.
Notice we don’t need tensile force, as it is not going to act on person. We are asked to explicitly find the force to accelerate person, not elevator.
Suppose you want to know the force needed to push up elevator overall:
Fnet= (mass) (acceleration) T-mg=ma T=m(a+g) T=(1050)(2+10) T= 12,600 Newtons
A man pulls a 100 kg crate via a rope angled 30 degrees above horizontal with a force of 200N. There is no friction force. What acceleration does the crate experience?
What are the forces involved?
Acceleration is on X axis. , as Force and acceleration are in the same direction.
The forces involved are
1) F of gravity
2) F normal force
3) Tension Force at 30 degrees
So F(net-x) =MA(x)
There is an X direction in the tension force.
so
200(cos30)=100(Ax)
Ax=(3)^.5
What are essential angles and trig functions?
0,30,45,60,90,180
What is Newton’s 3rd Law?
For every action, there is an equal and opposite reaction
What is Newtons’ 1st law
Law of inertia
What is newton’s 2nd law?
Acceleration if dependent on two variables, the net force acting on the object and the mass of the object .
What is the reaction force to the force of gravity acting on the person?
The reaction force ha to be from the same source (so both have to be same type of force) , and acts on two objects who are “squeezed together”
if the first force is acting on the person, it is arising from the ground
So the pair would be the Force of gravity on the person, and the Gravitational force of the person on Earth.
But the person does not exactly pull the earth towards it, as the person’s mass is way less than earth.
When does a force stop acting on an object?
When you lose contact with the object.
How do you know to use Newton’s 2nd or 3rd law?
1 object: 2nd law
2 objects: 3rd law
Friction is:
force between two solid surfaces that resist slipping motion between them
What is kinetic friction?
F(f,k)=ukF(normal)
Use it during skidding or slipping
Direction opposes velocity
What is static friction?
Static Friction is used when there is no motion, direction opposes other forces.
F(f,s) is equal to or less than UsF(n).
Exists only when you are attempting to move an object
If you apply a 8n force on a 5 kg block, what is force of friction acting on the block?
F(fs) is less than or equal to Us(Fn), which equals to
(0.3)(mg)=(0.3)(50 Newtons)=15 Newtons.
so nothing will happen
What if you apply 20 N force on the same block?
Now, you have to use kinetic friction, as you know previously that this is enough to overcome static friction.
What is the coefficient for static friction?
0.3
What is the coefficient for kinetic friction?
0.2
Is it possible for a moving object to experience a static frictional force?
Kinetic friction happens when surfaces are sliding past each other, not necessarily dependent on if object attached is moving.
An example is a wheel. When a wheel is rolling across a road, it is static friction, as the wheel is not “sliding”. Sliding wheels are much much harder to stop, as this means you have to overcome kinetic friction, which is much higher than static friction.
