Question

A heavy ball is hung from the ceiling by a steel wire. The instructor pulls the ball back and stands against the wall with the ball against his chin. To avoid injury, the instructor is supposed to release the ball without pushing it (Fig. 6–33). Why?

Short answer

When the ball is released without pushing, it will not hit the instructor.

Step-by-step solution

Understanding the change in energy of the ball

As soon as a certain object is released from a given height, its potential energy gets converted into kinetic energy.

Evaluation of the ball hitting the instructor without pushing it

An instructor uses a heavy ball hung from the ceiling through a steel wire to check whether he will get injured by releasing the ball with or without pushing it.

In the first case, if the ball is not pushed, it will lose some amount of energy to friction and air resistance, but it will not injure the instructor.

On the other hand, if the ball is pushed while releasing, it will have some kinetic energy initially and during its return. Thus, the ball will hit the instructor on the chin.