List two different situations in which a force exerted on an object does no work on the object. 

2) Can the centripetal force on an object undergoing uniform circular motion do work? If so, give an example. If not, why not? Hint: Think of the circular arc as a succession of very many short straight-line paths joined together. 

3) A winch is used to raise a heavy piano a given height, using a ramp. For a frictionless ramp, does the winch do more work if the ramp is steeper or if the ramp is more gradual? Why? 

4) When a \"superball\" is dropped, can it rebound to a height greater than its original height? Explain.