You are to design a rotating cylindrical axle to lift 800-n buckets of cement from the ground to a rooftop 78.0 m above the ground. the buckets will be attached to a hook on the free end of a cable that wraps around the rim of the axle; as the axle turns, the buckets will rise. part a what should the diameter of the axle be (in units of cm) in order to raise the buckets at a steady 2.00 cm/s when it is turning at 7.5 rpm?