A grinder consists of a solid 15 kg disk with a diameter of 57 cm. A when active, the disk rotates at a rate of 83 rad/sec. When its power is turned off, the disk comes to a rest after having rotated 21 times.
A/ What is the rate of angular acceleration of the disk during this process?
B/ What is the magnitude of the torque due to friction acting on the disk during this process?