a 50.0-kg grindstone is a solid disk 0.520 m in diameter. you press an ax down on the rim with a normal force of 160 n. the coefficient of kinetic friction between the blade and the stone is 0.60, and there is a constant friction torque of 6.50 n*m between the axle of the stone and its bearings. a. how much force must be applied tangentially at the end of a crank handle 0.500 m long to bring the stone from rest to 120 rev/min in 9.00 s? b. after the grindstone attains an angular speed of 120 rev/min, what tangential force at the end of the handle is needed to maintain a constant angular speed of 120 rev/min? c. how much time does it take the grindstone to come from 120 rev/min to rest if it is acted on by the axle friction alone?