Chapter 11, Problem 72GP

A 70 kg person stands on a tiny rotating platform with arms outstretched. (a) Estimate the moment of inertia of the person using the following approximations: the body (including head and legs) is a 60-kg cylinder, 12 cm in radius and 1.70 m high: and each arm is a 5.0-kg thin rod, 60 cm long, attached to the cylinder, (b) Using the same approximations, estimate the moment of inertia when the arms are at the person’s sides, (c) If one rotation takes 1.5 s when the person’s arms are outstretched, what is the time for each rotation with arms at the sides? Ignore the moment of inertia of the lightweight platform. (d) Determine the change in kinetic energy when the arms are lifted from the sides to the horizontal position. (e) From your answer to part (d), would you expect it to be harder or easier to lift your arms when rotating or when at rest?