a
6.4 kg disc rotates with initial angular velocity 18700rpm. a
worker shuts off the electrical switch and the disk comes to rest
with constant acceleration produced by frction torque of 1.4 m*N.
the radius of the disk is 0.23 m. moment of inercia: mR^2/2.
calculate the time of the first 390 full rotations of the disk,
after switch shuts off.