Two weights, one of mass 15 kg and the other of mass 9 kg, hang from a pulley by a massless
rope. The pulley has a mass of 6 kg and a radius of 4 cm. The weights are released from rest such
that the 15 kg weight begins to drop. How long will it take the weight to reach the ground 3.5 m
below? Assume that the rope does not slip and is long enough that the other weight does not
crash into the pulley.