Momentum - Conceptual Questions

For an elastic collision, which of the following statements are true?

- Momentum is conserved. - Kinetic energy is conserved.

For an INELASTIC collision, which of the following statements are true?

- Momentum is conserved. - Kinetic energy is gained or lost.

When a constant force acts on an object, what does the object's change in momentum depend upon?

- The change in momentum depends upon the time interval during which the force acts. - The change in momentum depends upon the magnitude of the force.

A 5-kg ball collides inelastically head-on with a 10-kg ball, which is initially stationary. Which of the following statements is true?

- The magnitude of the change of velocity the 5-kg ball experiences is greater than that of the 10-kg ball. - The magnitude of the change of the momentum of the 5-kg ball is equal to the magnitude of the change of momentum of the 10-kg ball.

Which of the following statements are true? Select all correct responses.

- The vector sum of forces acting on a particle equals the rate of change of momentum of the particle with respect to time. - The total momentum of any number of particles is equal to the vector sum of the momenta of the individual particles. - The total momentum of an isolated system is constant.

If a quantity you calculated had units of kg • m/s, what type of quantity could it be?

- momentum - impulse

A tiger is running in a straight line. If we double both the mass and speed of the tiger, the magnitude of its momentum will increase by what factor?

4

If you want to double the momentum of a gas molecule, by what factor must you increase its kinetic energy?

4

You are standing on a skateboard, initially at rest. A friend throws a very heavy ball towards you. You have two choices about what to do with the ball: either catch the ball or deflect it back toward your friend with the same speed as it was originally thrown. Which choice should you make in order to maximize your speed on the skateboard?

Deflect the ball back.

Which of the following quantities are units of momentum/impulse?

N*S kg*m/s

A very light ping-pong ball moving east at a speed of 4 m/s collides with a very heavy stationary bowling ball. The Ping-Pong ball bounces back to the west, and the bowling ball moves very slowly to the east. Which object experiences the greater magnitude impulse during the collision?

Neither; both experienced the same magnitude impulse.

A firecracker explodes in midair and breaks up into many fragments. Which of the following statements are true regarding conditions immediately before and immediately after the explosion:I. The total momentum of the fragments is equal to the original momentum of the firecracker.II. The total kinetic energy of the fragments is equal to the original kinetic energy of the firecracker.

Statement I only

A lump of putty and a rubber ball have equal mass. Both are thrown with equal speed against a wall. The putty sticks to the wall. The ball bounces back at nearly the same speed with which it hit the wall. Which object experiences the greater momentum change?

The ball experiences the greater momentum change.

Choose the best explanation from among the following:

The change in momentum when a bullet rebounds is larger than when it is brought to rest.

Consider two less-than-desirable options. In the first you are driving 30 mph and crash head-on into an identical car also going 30 mph. In the second option you are driving 30 mph and crash head-on into a stationary brick wall. In neither case does your car bounce back from the thing it hits, and the collision time is the same in both cases. Which of these two situations would result in the greater impact force on your car?

The force would be the same in both cases.

What represents the impulse of the force in a graph of force versus time?

The impulse is equal to the area under the curve.

In a lab environment, you are investigating the impulse of a force exerted on a brick when the brick's speed is reduced from 2.5 m/s to a complete stop. First, you allow the brick to slam into a secured piece of wood, bringing the brick to a sudden stop. Second, you allow the brick to plow into a large slab of gelatin so that the brick comes to a gradual halt. In which situation is there a greater impulse of the force on the brick?

The impulse is the same in both situations.

A very elastic rubber ball is dropped from a certain height and hits the floor with a downward speed v. Since it is so elastic, the ball bounces back with the same speed v going upward. Which of the following statements about the bounce are correct?

The magnitude of the ball's momentum was the same just before and just after the bounce.

A small car meshes with a large truck in a head-on collision. Which of the following statements concerning the momentum during the collision are correct?

The momentum of the car-truck system is conserved, but the momentum of each one separately is not conserved.

A rocket explodes into two fragments, one 25 times heavier than the other. The magnitude of the momentum change of the lighter fragment is

The same as the momentum change of the heavier fragment.

A small car meshes with a large truck in a head-on collision. Which of the following statements concerning the magnitude of the average force during the collision is correct?

The small car and the truck experience the same average force.

A small car meshes with a large truck in a head-on collision. Which of the following statements concerning the magnitude of the momentum change during the collision is correct?

The small car and the truck experience the same magnitude momentum change.

A freight car moves along a frictionless level railroad track at constant speed. The freight car is open on the top. A large load of sand is suddenly dumped into the freight car. What happens to the speed of the freight car?

The speed of the freight car decreases.

When a person steps forward out of a small boat onto a dock, the boat recoils backward in the water. Why does this occur?

The total momentum of the system is conserved.

A red ball with a velocity of +3.0 m/s collides head-on with a yellow ball of equal mass moving with a velocity of −2.0 m/s. What is the velocity of the two balls after the elastic collision?

The velocity of the red ball is −2.0 m/s; the velocity of the yellow ball is +3.0 m/s.

Three cars, car X, car Y, and car Z, begin accelerating from rest at the same time. Car X is more massive than car Y, which is more massive than car Z. The net accelerating force exerted on each car is identical. After 10 seconds, which car has the most amount of momentum?

They all have the same amount of momentum.

In a collision between two unequal masses, which mass receives a greater magnitude impulse?

They receive equal impulses.

A block of wood is struck by a bullet. Is the block more likely to be knocked over if the bullet is metal and embeds itself in the wood, or if the bullet is rubber and bounces off the wood?

bullet is rubber and bounces off the wood

In a game of pool, the white cue ball hits the #5 ball and stops, while the #5 ball moves away with the same velocity as the cue ball had originally. Both balls have the same mass. This type of collision is

elastic.

Identical forces act for the same length of time on two different objects. The magnitude of the change in momentum of the lighter object is

exactly equal to the magnitude of the change in momentum of the larger mass.

In an inelastic collision involving an isolated system, the final total momentum is

exactly the same as the initial momentum.

The momentum of an isolated system is conserved

in both elastic and inelastic collisions.

A railroad car collides with and sticks to an identical railroad car that is initially at rest. After the collision, the kinetic energy of the system

is half as much as before.

An egg falls from a bird's nest in a tree and feels no effects due to the air. As it falls,

only its mechanical energy is conserved.

On a horizontal frictionless air table, a puck runs into an ideal horizontal spring that is fastened to the table. The puck compresses the spring by 15 cm before coming to rest. During the compression process, which quantities are conserved?

only the mechanical energy (kinetic plus potential) of the puck

If you want to double the kinetic energy of a gas molecule, by what factor must you increase its momentum?

square root of 2

Two friends are standing on opposite ends of a canoe that is initially at rest with respect to a frictionless lake. The person in the front throws a very massive ball toward the back, and the person in the back catches it. After the ball is caught, the canoe is

stationary.

A rubber ball and a lump of clay have equal mass. They are thrown with equal speed against a wall. The ball bounces back with nearly the same speed with which it hit. The clay sticks to the wall. Which one of these objects experiences the greater momentum change?

the ball

Two objects of different mass have equal, non-zero kinetic energies. Which object has the greater magnitude momentum?

the heavier object

A rubber ball bounces off of a wall with an initial speed v and reverses its direction so its speed is v right after the bounce. As a result of this bounce, which of the following quantities of the ball are conserved?

the kinetic energy of the ball

Two objects of different masses have momentum of equal, non-zero magnitude. Which object has more kinetic energy?

the lighter object

During World War I, Germany used a "Big Bertha" cannon to hurl shells into Paris 30 miles away. This gun also had a very long barrel. What was the reason for using a long barrel in these guns?

to allow the force of the expanding gases from the gunpowder to act for a longer time