The Ultimate Physics Preparation Test On Impulse And Momentum!

1. Which of the following involves a change in momentum?

An ice skater moves down the rink at a constant speed.

A newspaper delivery boy travels at a constant speed while “losing” mass by throwing his newspapers on porches.

A car coasts down a hill at a constant speed.

A child rides a tricycle at a constant speed.

In this scenario, the newspaper delivery boy is experiencing a change in momentum. As he throws newspapers on porches, he is exerting a force in the opposite direction, causing a change in his momentum. According to Newton's third law of motion, for every action, there is an equal and opposite reaction. Therefore, the force exerted by the delivery boy throwing the newspapers results in a change in his momentum.

Explanation

In this scenario, the newspaper delivery boy is experiencing a change in momentum. As he throws newspapers on porches, he is exerting a force in the opposite direction, causing a change in his momentum. According to Newton's third law of motion, for every action, there is an equal and opposite reaction. Therefore, the force exerted by the delivery boy throwing the newspapers results in a change in his momentum.

2. A person rolls off of a raft while in the pool, which causes the raft to float away from the person. The momentum of the raft:

Remained the same.

Was zero while stationary and increased when the person got off.

Was greatest while the person laid on it.

Was zero when the person got off of the raft and increased while the person was on the raft.

When the person is on the raft, both the person and the raft are in motion together. The momentum of the system (person + raft) is not zero. However, when the person gets off the raft, the momentum of the system changes. The person's momentum becomes zero as they are no longer in motion, but the raft continues to move in the opposite direction, causing its momentum to increase. Therefore, the correct answer is that the momentum of the raft was zero while stationary and increased when the person got off.

Explanation

When the person is on the raft, both the person and the raft are in motion together. The momentum of the system (person + raft) is not zero. However, when the person gets off the raft, the momentum of the system changes. The person's momentum becomes zero as they are no longer in motion, but the raft continues to move in the opposite direction, causing its momentum to increase. Therefore, the correct answer is that the momentum of the raft was zero while stationary and increased when the person got off.

3. When a baseball bat hits a baseball, the change in momentum of the bat is_______the change in momentum of the ball.

Less than

Greater than

Equal to

None of the answers

When a baseball bat hits a baseball, the change in momentum of the bat is equal to the change in momentum of the ball. This is because of the law of conservation of momentum, which states that the total momentum of a system remains constant unless acted upon by an external force. Since the bat and the ball are part of the same system, the change in momentum of one object must be equal and opposite to the change in momentum of the other object.

Explanation

When a baseball bat hits a baseball, the change in momentum of the bat is equal to the change in momentum of the ball. This is because of the law of conservation of momentum, which states that the total momentum of a system remains constant unless acted upon by an external force. Since the bat and the ball are part of the same system, the change in momentum of one object must be equal and opposite to the change in momentum of the other object.

4. Two hockey players skate directly towards each other at the same velocity trying to get to the hockey puck. One of the skater's mass is 82 kg, and the other's mass is 75 kg. The hockey players crash into each other without spinning. Which of the following statements is true BEFORE the collision?

The lighter skater has less momentum.

Their momenta are equal but opposite.

The lighter skater has half of the momentum that the heavier skater has.

Their total momentum increases after the crash.

Before the collision, the two hockey players are moving towards each other at the same velocity. Momentum is defined as the product of an object's mass and its velocity. Since the lighter skater has a smaller mass compared to the heavier skater, it means that the lighter skater will have less momentum. Therefore, the statement "the lighter skater has less momentum" is true before the collision.

Explanation

Before the collision, the two hockey players are moving towards each other at the same velocity. Momentum is defined as the product of an object's mass and its velocity. Since the lighter skater has a smaller mass compared to the heavier skater, it means that the lighter skater will have less momentum. Therefore, the statement "the lighter skater has less momentum" is true before the collision.

5. A cannon fires a cannonball. Immediately after the cannonball is fired, which of the following is NOT true?

The cannon and the cannonball have the same magnitude of momentum.

The cannon and the cannonball have the same kinetic energy.

The explanation for the given correct answer is that the cannon and the cannonball do not have the same kinetic energy. Kinetic energy is determined by the mass and velocity of an object, and since the cannonball is smaller and lighter than the cannon, it will have a different kinetic energy. Additionally, the cannonball is the one being propelled forward by the explosion in the cannon, so it will have a higher velocity and therefore a greater kinetic energy than the cannon.

Explanation

The explanation for the given correct answer is that the cannon and the cannonball do not have the same kinetic energy. Kinetic energy is determined by the mass and velocity of an object, and since the cannonball is smaller and lighter than the cannon, it will have a different kinetic energy. Additionally, the cannonball is the one being propelled forward by the explosion in the cannon, so it will have a higher velocity and therefore a greater kinetic energy than the cannon.