Question

A grindstone of mass m = 50.0 kg is a solid disk 0.480 m in diameter. You press an ax down on the rim with a normal force of F = 155 N The coefficient of kinetic friction between the blade and the stone is 0.50, and there is a constant friction torque of 6.5 Nm between the axle of the stone and its bearings.

(a) While you are pressing the ax against the rim, how much force would your assistant need to apply tangentially at the end of a crank handle 0.5 m long to bring the stone from rest to 130 rev/min in 9.00 s? N

(b) After the grindstone attains an angular velocity of 130 rev/min, what tangential force at the end of the handle is needed to maintain a constant angular velocity of 130 rev/min? (The ax is still pressed against the rim.) N

(c) How much time does it take the grindstone to come from 130 rev/min to rest if it is acted on by the axle friction alone?

Answer 1