A prospector uses a hand-powered winch (see figure) to raise a bucket of ore in his mine

Question:

A prospector uses a hand-powered winch (see figure) to raise a bucket of ore in his mine shaft. The axle of the winch is a steel rod of diameter d = 0.625 in. Also, the distance from the center of the axle to the center of the lifting rope is b = 4.0 in.
If the weight of the loaded bucket is W = 100 lb, what is the maximum shear stress in the axle due to torsion?