CAST Practice 1

CAST Practice 1

By Christine Boudreau

Multiple Choice

At boxing practice, Nathan works with his coach to improve the strength of his punch. Nathan says that the reason the bag is heavy is so that it can absorb plenty of elastic potential energy. Is he correct?

• Yes, he is correct.

• No, the bag absorbs thermal energy.

• No, the bag absorbs gravitational potential energy.

• No, the bag is heavy so that its mass will only accelerate a small amount when he punches it.

Force = mass x acceleration.

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Thermal energy is ​the total energy of motion in the particles of a substance (it is heat energy).

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​Gravitational potential energy is potential energy that depends on the height of an object.

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​Explanation

Multiple Choice

Nathan lost his balance when he hit the bag with a hard punch. He says that was because of the reaction force from his punch, which was large because the bag is heavy. Is he correct?

• Yes, he is correct.

• No, it is not the weight, it is the large mass of the bag that gives the large reaction force.

• No, the reaction force depends on the force of Nathan's punch, not on the mass of the bag.

• No, the bag does not exert a reaction force, because it is flexible.

Newton's third law states that for every action there is an equal and opposite reaction.

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​Explanation

Fill in the Blanks

Nathan notices that when the bag moves away from him, it swings upward. Then, it slows to a stop and then swings back. Nathan knows that the

energy of the bag is converted to gravitational potential energy as the bag swings upward.

Fill in the Blanks

Marcia and her father are on a seesaw at a park. Since her father is heavier, he can only balance the seesaw if he sits closer to the pivot of the seesaw than Marcia does. Marcia has a mass of 40 kg. Her father has a mass of 80 kg. While the seesaw has a mass of 8 kg. The total gravitational force on Marcia, her father, and the seesaw is

Newtons downward.

Fill in the Blanks

When the seesaw is balanced, the force the pivot exerts on the seesaw is 1254 N in the

direction.

Fill in the Blanks

When the seesaw is balanced, the force the pivot exerts on the seesaw is 1254 N in the upward direction and the acceleration is

.