Question

Irving, a cat, has a favorite toy that is made up of a squeaky ball at the end of a string. The toy makes up a closed system. Irving’s owner dangles the toy so that the ball swings down and then swings back up again.

Ignoring any friction, how are kinetic and potential energy related to each other as the ball swings back and forth?

As the ball moves upward, both kinetic and potential energy decrease.
As the ball moves downward, both kinetic and potential energy increase.
As the ball moves upward, kinetic energy decreases and potential energy increases.
As the ball moves downward, kinetic energy decreases and potential energy increases.

Answer 1

As the ball swings down, it is losing potential energy since it is losing height. This lost energy is converted into kinetic energy which allows the ball to be able to swing back up on the other side. As the ball reaches the middle of the swing or when it gets to the very bottom, all of the potential energy is converted into kinetic energy. As the ball reaches its highest points as it stops to go the other direction, it loses all of its kinetic energy and is at its maximum potential energy.
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So basically the swinging of the ball is the conversion of kinetic and potential energies back and forth between each other. They both help each other swing the ball back and forth.

Answer 2

Answer: As the ball moves upward, kinetic energy decreases and potential energy increases.

Explanation:

In a closed system, the energy is conserved. It can convert from one form to another. Mechanical energy is the sum of kinetic energy and potential energy.

M.E. = K.E. + P.E.

A body possesses kinetic energy due to virtue of its motion.

K.E. = 0.5 m v²

Potential energy is possessed by a body due to virtue of its position.

P.E. = m g h

The sum of kinetic energy and potential energy remains constant.

K.E. + P.E. = constant

Thus, when the ball moves upwards, potential energy increases thereby decreasing its kinetic energy.