A fly-wheel of mass 12 kg and radius 20 cm is mounted on the light horizontal axle of radius 5cm that rotates on frictionless bearings. A string wound about the axle has joined to its free end a hanging mass of 4kg, and the system is permitted to began from rest. When the string leaves the axle after the mass has descended 3m, determine what torque should be applied to the flywheel to bring it to rest in the 5 revs?