You have a horizontal grindstone (a disk) that is 87 kg, has a 0.33 m radius, is turning at 93 rpm (in the positive direction), and you press a steel axe against the edge with a force of 25 N in the radial direction. Assuming that the kinetic coefficient of friction between the steel and stone is 0.20, calculate the angular acceleration of the grindstone in rad/s^2.