[CQ] Physics Honors - Momentum

How is a cargo ship traveling at around 5 mph able to completely collapse a bridge when it collides with it?

It's mass is massive, which means it has a lot of momentum, making it difficult to stop.

True/False: If an object is in motion, then it has momentum.

True

Momentum

A mass in motion.

Momentum depends on what two things?

Mass and velocity.

What equation(s) can be used to find momentum?

mv

What is the unit for momentum?

kg ⋅ m/s

Momentum is a...
A. Vector (Magnitude + Direction).
B. Scalar (Only Magnitude).

A

Which has more momentum?
A. A large truck moving at 30 m/s.
B. A small car moving at 30 m/s.
C. They both have the same momentum.

A

What equation(s) can be used to find the momentum of the system?

p₁ + p₂ + p₃ + p₄ + ...
m₁v₁ + m₂v₂ + m₃v₃ + m₄v₄ + ....

Vector Sum

The direction of the velocity of each object in a system.

How do you stop an object with momentum?

A force needs to be applied for a given period of time.

What equation(s) can be used to find the change of momentum?

mΔv
Ft

Impulse

The quantity of force times time.

What is the unit for impulse?

Newton Seconds (Ns)

True/False: Impulse = Change in Momentum

True

A change in momentum in a short time requires a large or small force?

Large

A change in momentum in a long time requires a large or small force?

Short

Air bags are used in cars because they __________________________________________________________________________________________________________.
A. increase the force with which you hit the dashboard
B. increase the duration (time) of impact in a collision
C. decrease the momentum of a collision
D. decrease the impulse in a collision

B

One car crashes in a concrete barrier. Another car crashes into a collapsible barrier at the same speed. What is the difference between the 2 crashes?
A. Change in momentum.
B. Force on the car.
C. Impact time.
D. Both B and C are true.

B

How do you find impulse on a graph of force as the y-axis and time as the x-axis?

Find the area under the line.

How can you change the momentum of a system?

By applying an impulse.

If a system has some initial energy, pᵢ, doing impulse on it will change the momentum, to make a new value, pf. What formula does this result in?

pᵢ + I = pf

What can pᵢ = pf be rewritten as?

m₁v₁ + m₂v₂ = m₁v₁ + m₂v₂

Momentum will remain unchanged or conserved when there's no impulse (no external force). What equation does this result in?

pᵢ = pf

Isolated System

A system where objects can interreact with each other by colliding. If they are stuck together, they can explode, push apart. Both momentum and total energy is conserved, but energy can change from one type to another.

Which of the following is required for momentum to be conserved in a system?
A. The system must be an open system, acted upon by external positive forces.
B. The system must be an open system, acted upon by external negative forces.
C. Either positive or negative outside forces may act.
D. No net external forces can act on the system.

D

Explosions

When an object or objects breaks apart because potential energy in one or more of the objects is transformed into kinetic energy. Since there are no external forces acting on the object, momentum is conserved but kinetic energy is not.

Inelastic Collisions

When two objects collide, converting some kinetic energy into other forms of energy such as potential energy, heat, or sound. Since there are no external forces acting on the object, momentum is conserved but kinetic energy is not.

Elastic Collisions

When two objects collide and bounce off each other while conserving kinetic energy. Energy is not transformed into any other type of energy. Since there are no external forces acting on the object, momentum and kinetic energy is conserved.

Prime (')

After.

Why is a firecracker an example of an explosion?

The chemical potential energy inside of it is transformed into kinetic, light, and sound energy.

Why is a cart with a compressed spring an example of an explosion?

When the spring is against a wall and gets released, the cart starts to move, converting elastic potential energy to kinetic and sound energy.

What equation(s) can be used for explosions?

(m₁ + m₂)v = m₁v₁' + m₂v₂'

Perfectly Inelastic Collisions

When two objects collide and stick together and start moving afterward as one object.

What equation(s) can be used for perfectly inelastic collisions?

m₁v₁ + m₂v₂ = (m₁ + m₂)v'

True/False: Explosions and inelastic collisions are the exact same thing.

False

In ______ collisions, momentum is conserved.
A. elastic
B. inelastic
C. all

C

In ______________ collisions, kinetic energy is conserved.
A. elastic
B. inelastic
C. all

A

What equation(s) can be used for elastic collisions?

v₁ - v₂ = -(v₁' - v₂')

Relative Velocity

All elastic collisions, independent of each object's mass, the magnitude of this of the objects is the same before and after the collision.

What are the cases of elastic collisions?

When two particles of equal mass collide, when a heavy particle collides with a light particle at rest, and when a light particle collides with a heavy particle at rest.

What can be predicted in a situation where two particles of equal mass collide elastically?

They exchange velocities.

What can be predicted in a situation where one, much heavier particle collides with a lighter particle at rest ellastically?

The larger mass continues moving with almost the same velocity, while the small mass moves at twice the initial speed of the larger mass.

What can be predicted in a situation where one, much lighter particle collides with a much heavier particle at rest elastically?

The smaller mass moves with the same speed but in the opposite direction. The larger mass remains mostly at rest.

A bowling ball has a velocity of +v when it collides with a ping pong ball that is at rest. The velocity of the bowling ball is virtually unaffected by the collision. What will be the speed of the ping pong ball?
A. 0v
B. 1v
C. 2v
D. 4v

C

A baseball bat has a velocity of +v when it collides with a baseball that has a velocity of -2v. The bat barely changes velocity during the collision. How fast is the baseball going after it's hit?
A. -1v
B. 0v
C. 3v
D. 4v

D

Object I is moving East. Object II is also moving East. Which of the following is the net momentum of the system of two objects?
A. ⬅
B. ⬈
C. ⬊
D. ⬋
E. ⮕

E

A cannon fires a cannonball and recoils backward. Which of the following statements is true about the cannon recoil?
A. It happens because the energy of the system is conserved.
B. It happens because the energy of the system is increased.
C. It happens because the momentum of the system is not conserved.
D. It happens because the momentum of the system is conserved.
E. It happens because the momentum of the system is increased.

D

Object II is moving West at a greater velocity. Object I is moving East. Which of the following is the net momentum of the system of two objects?
A. ⬅
B. ⬈
C. ⬊
D. ⬋
E. ⮕

A

An air balloon hovers at a certain altitude above the ground. A pilot throws a sandbag down from the balloon. What is the direction of the balloon's velocity just after the bag was thrown?
A. ⮕
B. ⬈
C. ⬊
D. ⬅
E. ⬆

E

What is the momentum of the cannon after firing a cannonball with an initial momentum of 5,000 kg ⋅ m/s to the right?
A. 5,000 kg ⋅ m/s to the right
B. 5,000 kg ⋅ m/s to the left
C. zero
D. 2,500 kg ⋅ m/s to the right
E. 2,500 kg ⋅ m/s to the left

B

A platform moves at a constant velocity on a constant velocity on a horizontal surface. What happens to the velocity of the platform after a sudden rain falls down?
A. It increases because the energy is conserved.
B. It decreases because the energy is conserved.
C. It remains constant because the momentum is conserved.
D. It increases because the momentum is conserved.
E. It decreases because the momentum is conserved.

E

A stationary skateboarder I with a mass of 50 kg pushes a stationary skateboarder II with a mass of 75 kg. After the push the skateboarder II moves with a velocity of 2 m/s to the right. What is the velocity of the skateboarder I?
A. 3 m/s to the left
B. 2 m/s to the left
C. 1 m/s to the right
D. 3 m/s to the right
E. 2 m/s to the right

A

When two objects collide elastically the momentum is conserved. Which of the following is true about the kinetic energy during the collision?
A. The kinetic energy is conserved.
B. The kinetic energy is lost.
C. The kinetic energy is gained.
D. The kinetic energy completely transforms into thermal energy.

B

A light beach ball moving with a velocity 2 m/s to the right collides elastically with a stationary bowling ball. After the collision the bowling ball remains stationary. What is the velocity of the beach ball after the collision?
A. 0 m/s
B. 2 m/s to the left
C. 4 m/s to the left
D. 3 m/s to the left
E. 1 m/s to the left

B

A bowling ball moving with a constant speed, v, collides elastically with a stationary beach ball. After the collision the bowling ball barely slows down. What is an approximate speed of the beach ball after the collision?
A. v
B. ½v
C. ⅓v
D. 2v
E. 3v

D

A big truck collides inelastically with a small car. Which of the following statements is true?
A. The truck experiences the greater magnitude of impulse during the collision.
B. The car experiences the greater magnitude of impulse during the collision.
C. They experience the same magnitude of impulse during the collision.
D. The impulse of each object is zero during the collision.

C

When mass A collides with and sticks to mass B, this is an example of ____________________________________________.
A. an elastic collision
B. an explosion
C. an inelastic collision
D. could be either an elastic or inelastic collision

C

When mass A collides with and sticks to mass B, this is an example of ________________________________________________________________________________.
A. an elastic collision
B. an explosion
C. an inelastic collision
D. either an elastic or inelastic collision

D

When mass A collides elastically with mass B, ____________________________________________________________________________________________.
A. kinetic energy is conserved
B. momentum is conserved
C. both kinetic energy and momentum are conserved
D. neither momentum nor kinetic energy are conserved

C

If an object is stationary, __________________________________________________________________________________________.
A. its momentum is zero
B. its kinetic energy is zero
C. both its momentum and kinetic energy are zero.
D. neither its momentum nor kinetic energy are zero

C

When mass A collides and sticks to a stationary mass B, their combined velocity after ______________________________________________________________________.
A. will be greater than mass A's velocity
B. will be less than mass A's velocity
C. will be zero
D. cannot be determined

B

A sand bag is thrown out of a hovering hot air balloon. This is an example of an __________________.
A. elastic collision
B. inelastic collision
C. explosion
D. not enough information to decide

C

A sandbag is thrown out of a hovering hot air balloon. Which statement is true about the sandbag/balloon system?
A. Momentum is the same before and after the bag is thrown.
B. Kinetic energy is the same before and after the bag is thrown.
C. Both momentum and kinetic energy change.
D. Neither momentum nor kinetic energy change.

A

A ball moving horizontally bounces off a wall and moves in the opposite direction. The impulse of the ball ______________________________________________________________________.
A. is equal to the impulse on the wall
B. is smaller than the impulse on the wall
C. is greater than the impulse on the wall
D. is zero

A

A truck moving at a constant velocity has a heavy load dropped onto it. What happens to the velocity of the truck?
A. It increases because momentum is conserved.
B. It decreases because momentum is conserved.
C. It increases because kinetic energy is conserved.
D. It decreases because kinetic energy is conserved.

B