Physics Questions on Kinetic Energy

During a game of pool, the cue ball is rolling toward the eight ball that is at rest. Preeta claims that all of the kinetic energy in the cue ball will get transferred to the eight ball after they collide. Which graph best supports Preeta’s claim?

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Which energy transfer diagram represents the racquetball and basketball demonstration?

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Why did the racquetball bounce higher when bouncing from the basketball than when it was originally dropped?

• a. The racquetball bounced higher because it started from a higher position on the basketball.

• b. Both the racquetball and the basketball had increased kinetic energy when they were bounced together.

• c. The racquetball bounced higher because energy was transferred to it from the basketball. The basketball then bounced lower than it did on its own.

• d. The racquetball bounced to the same height regardless of where it starts.

Answer explanation

The racquetball bounced higher because it received energy from the basketball during the collision. This energy transfer allowed the racquetball to achieve a greater height than when it was dropped alone.

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Lily and Ava are studying energy conservation in their physics class. They are trying to understand what could be considered a system where energy stays the same. What could be considered a system? More than one answer is possible.

• a. One object

• b. Two objects

• c. Any number of objects

• All of the above

Answer explanation

A system can be defined as any collection of objects where energy is conserved. This includes one object, two objects, or any number of objects. Therefore, the correct answer is 'All of the above'.

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The diagram shows how one type of energy can be converted to another type of energy. In this case, KE is converted to GE which gets converted back to KE. The racquetball/basketball demonstration showed that energy can also be transferred from one object to another within a system. Consider the pendulum and the surrounding air molecules as a system. Which energy transfer diagram shows what causes the pendulum to slow down and eventually stop?

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What causes the pendulum to slow down and eventually stop?

• The pendulum slows down and eventually stops because it transfers kinetic energy to the surrounding air molecules.

• The pendulum slows down and eventually stops because gravity pulls it down toward the center of the Earth.

• The GE of the pendulum gets transferred to the air around the pendulum and causes it to stop.

Answer explanation

The correct choice explains that the pendulum slows down due to the transfer of kinetic energy to surrounding air molecules, leading to energy loss and eventual stop, rather than gravity or potential energy transfer.

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Why does a ball stop bouncing?

• Each time a ball hits the floor the KE gets converted to GE and some is lost to gravity. The GE gets transferred to KE and then to Elastic Energy. Friction also plays a role.

• The ball stops bouncing because each time it strikes the ground some of its energy is transferred to the surroundings, so less remains for the ball. This continues until none remains for the ball and then it stops.

• The ball stops bouncing because each time it strikes the floor the elastic energy absorbs the shock. The KE and GE decrease over time until it slows down and stops.

Answer explanation

The ball stops bouncing because each time it strikes the ground, some energy is lost to the surroundings. This energy loss continues until there is none left for the ball, causing it to stop.

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What happens to the energy of a ball when it is thrown upwards?

• b. The gravitational potential energy increases as the ball moves upwards.

• c. The energy remains constant as the ball moves upwards.

• a. The kinetic energy increases as the ball moves upwards.

• d. The energy is lost to the surroundings as the ball moves upwards.

Answer explanation

When a ball is thrown upwards, it gains height, which increases its gravitational potential energy. The kinetic energy decreases as the ball slows down, but the total mechanical energy remains constant in the absence of air resistance.

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How does friction affect the motion of a sliding object?

• a. Friction increases the speed of the sliding object.

• b. Friction decreases the speed of the sliding object.

• c. Friction has no effect on the speed of the sliding object.

• d. Friction converts kinetic energy into potential energy.

Answer explanation

Friction opposes the motion of sliding objects, causing them to slow down. Therefore, the correct answer is b: Friction decreases the speed of the sliding object.

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Why does a compressed spring have potential energy?

• c. Because it is in contact with the ground.

• d. Because it is made of elastic material.

• b. Because it has the ability to do work when released.

• a. Because it is at rest and not moving.

Answer explanation

A compressed spring has potential energy because it can do work when released. The stored energy is due to its position and the elastic properties of the material, allowing it to exert force and perform work.

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