Physics Quiz 4

In a collision between two objects having unequal masses, how does magnitude of the impulse imparted to the lighter object by the heavier one compare with the magnitude of the impulse imparted to the heavier object by the lighter one?

Both objects receive the same impulse

You are standing on a skateboard, initially at rest. A friend throws a very heavy ball towards you. You can either catch the object or deflect the object back towards your friend (such that it moves away from you with the same speed as it was originally thrown). What should you do in order to MINIMIZE your speed on the skateboard?

Catch the ball

A system that has zero momentum must also have zero kinetic energy.

False

There must be equal amounts of mass on both side of the center of mass of an object.

False

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

It decreases

On a smooth horizontal floor, an object slides into a spring which is attached to another mass that is initially stationary. When the spring is most compressed, both objects are moving at the same speed. Ignoring friction, what is conserved during this interaction?

Momentum and mechanical energy

A Ping-Pong ball moving east at a speed of 4 m/s, collides with a 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 rubber ball and a lump of putty 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 putty sticks to the wall. Which objects experiences the greater momentum change?

The ball

Jacques and George meet in the middle of a lake while paddling in their canoes. They come to a complete stop and talk for a while. When they are ready to leave, Jacques pushes George's canoe with a force to separate the two canoes. What is correct to say about the final momentum and kinetic energy of the system?

The final momentum is zero kgm/s but the final kinetic energy is positive.

A tennis ball undergoes an elastic collision when it hits the ground and bounces up. It is given that the speed of the ball just before it hits the ground is -v0 and immediately after rebounding it is +v0. Which of the statements below is true?

The momentum of the ball changes and the momentum of Earth also changes by the same amount.

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

The small car and the truck experience the same average force

A 3.0-kg object moves to the right at 4.0 m/s. It collides head-on with a 6.0-kg object moving to the left at 2.0 m/s. Which statement is correct?

The total momentum both before and after the collision is zero.

The center of mass of an object does not have to be located within the object.

True

In a perfectly ELASTIC collision between two perfectly rigid objects

both the momentum and the kinetic energy of the system are conserved.

Identical forces act for the same length of time on two different masses. The change in momentum of the smaller mass is

equal to the change in momentum of the larger mass.

A railroad car of mass m and speed v collides 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

You are standing at a bus stop holding an umbrella on a rainy day. While you wait for the bus the rain shower turns into hail. Compared to the rain, the number of hail "drops" hitting the umbrella per second, the mass of the "drops", and their speed all remain the same. The force you must exert to hold the umbrella in the hail is

more than the force required in the rain.

An artillery shell 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 shell. II. The total kinetic energy of the fragments is equal to the original kinetic energy of the shell.

statement I only

A shell explodes into two fragments, one fragment 25 times heavier than the other. If any gas from the explosion has negligible mass, then

the momentum change of the lighter fragment is exactly the same as the momentum change of the heavier fragment.

In an INELASTIC collision between two objects

the momentum of the system is conserved but the kinetic energy of the system is not conserved.