A $60\mathrm{.}0$ kg grindstone is a solid disk $0\mathrm{.}510$ m in diameter. You press an ax down on the rim with a normal force of F $=180$ N $($Figure $1).$ The coefficient of kinetic friction between the blade and the stone is $0\mathrm{.}60,$ and there is a constant friction torque of $6\mathrm{.}50$ N$$m between the axle of the stone and its bearings.

Part A

How much force must be applied tangentially at the end of a crank handle $0\mathrm{.}500$ m long to bring the stone from rest to $120$ rev$/$min in $7\mathrm{.}00$ s$?$

Part 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$?$

Part 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?