calculate…..

A disc of mass 290 grams and radius 12.0 cm is rotating about an axis passing through its center at 500 rpm. From a height of 15.0 cm, another disc, of mass 320 grams and radius 12.0 cm is dropped and both the discs start to rotate together.
The disc, which is dropped has some rough padding on it, which creates some frictional torque.
(a)Find the angular velocity of the discs as soon as they start to rotate.
(b)Using the fact that work done by the non-conservative forces changes the total mechanical energy of a system, find the frictional torque acting between the discs when they complete one revolution.
(c)Calculate the angular deacceleration of the disc, assuming the frictional torque calculated in part (b) is constant.
(d)How long will the discs take to complete 4 revolutions