The four 3-kg balls are rigidly mounted to the rotating frame and shaft, which are initi...

The four 3-kg balls are rigidly mounted to the rotating frame and shaft, which are initially rotating freely about the vertical z-axis at the angular rate of 20 rad/s clockwise when viewed from above. If a constant torque M = 30 N·m is applied to the shaft, calculate the time t to reverse the direction of rotation and reach an angular velocity in the same sense as M.