A flywheel of mass 12kg and radius 20cm is mounted on a light horizontal axle of radius 5cm which rotates on frictionless bearings. A string wound around the axle has attached to its free end a hanging mass of 4kg, and the system is allowed to start from rest. If the string leaves the axle after the mass has descended 3m, what torque must be applied to the flywheel to bring it to rest in 5 revs?