physics momentum and collisions test

On a pool table, a moving cue ball collides with the eight ball, which is at rest. Is it possible for both balls to be at rest immediately upon colliding? Use the law of conservation of momentum to explain your reasoning.

No, the final momentum can equal zero only if the initial momentum was zero. Because the cue ball was moving, its initial momentum was not zero. Therefore, both balls cannot be at rest after the collision.

A moderate force will break an egg. Using the impulse-momentum theorem  (momentum, force, and time interval), explain why an egg is more likely to break when it is dropped on concrete than if it is dropped on grass.

Stopping a falling egg requires changing the momentum of the egg from its value at the time of first impact to zero. If the egg hits the concrete, the time interval over which this happens is very small, so the force is large. If the egg lands on grass, the time interval over which the momentum changes is larger, so the force on the egg is smaller.

How can a small force produce a large change in momentum?

if the force acts in an object for a long time

What is the relationship between impulse and momentum?

Impulse is equal to change in momentum

A rubber ball collides “perfectly elastically” with the sidewalk... does each object have the same kinetic energy after the collision as it has before the collision? Explain your answer.

No. If the collision is perfectly elastic, the total KE is conserved, but each object may gain or lose KE.

Two isolated objects have a head on collision... if you know the initial and final velocity of one object and the mass of the other object, do you have enough information to find the final velocity of the second object? You must explain your answer!

No, you do not have enough information. V2f also depends on knowing V2i and M1.

Consider a field of insects, all of which have essentially the same mass... if the momentum of the insects is zero, what does this imply about their motion?

Although each insect might be moving in a random fashion, the net velocity of all the insects MUST equal zero.

Give two examples of elastic collisions and two examples of perfectly inelastic collisions...

Elastic collisions: 1. 2 marbles hitting each other 2. a tennis ball hitting the ground

Perfectly inelastic: 1. a dart hitting a dartboard 2. a snowball hitting another snowball and sticking

Two isolated objects have a head on collision... if you know the masses and initial velocities of both objects and the final velocity of one object, do you have enough information to find the final velocity of other object? You must explain your answer!

Yes, using the conservation of momentum, you could substitute the values and solve for Vf.

The speed of a particle is doubled. By what factor is its momentum changed? Show... What happens to its kinetic energy? Sho

Momentum is increased by a factor of two. KE increases by a factor of 4.

A rubber ball collides “perfectly elastically” with the sidewalk... does each object have the same momentum after the collision as it has before the collision? Explain your answer.

No. If the collision is perfectly elastic, the momentum is conserved, but each object may gain or lose momentum.

Two isolated objects have a head on collision... if you know the masses of both objects and the final velocities of both objects, do you have enough information to find the initial velocities of both objects? You must explain your answer!

No. using the conservation of momentum, you could only find the relationship between Vi1 and Vi2.