Q: As an exercise for wrist, palm and fingers, a person squeezes and releases a rubber ball. Is the work done on the ball positive, negative or zero during (a) compression and (b) during expansion?
A: Work done on ball = Increase in elastic potential energy
Potential energy increases during compression (think of analogy with spring) and thus the work done is positive.
Potential energy decreases during expansion and thus the work done is negative.
