A grindstone used to sharpen tools is rotating at an angular speed of 8.00 rad/s when an axe is pressed against it. Because of the torque produced on the grindstone by the force of friction between it and the axe, it comes to rest in four rotations. There is negligible friction in the grindstone's bearings.
a. Find the frictional force produced, assuming the grindstone is a cylinder of mass 5.00 kg and radius 0.425 m.
b. If the coefficient of friction between the axe and grindstone is 0.320, find the normal force with which the axe was pressed against the grindstone.