A $65\mathrm{.}0$ kg

grindstone is a solid disk $0\mathrm{.}550$ m

in diameter. You press an ax down on the rim with a normal force of F

$=140$ 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. 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 $8\mathrm{.}00$ s$?$ 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$?$ 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?