You have a grindstone $($a disk$)$ that is $85\mathrm{.}0$ kg$,$ has a $0\mathrm{.}400-$m radius, and is turning at $87\mathrm{.}0$ rpm$,$ and you press a steel axe against it with a radial force of $14\mathrm{.}0$ N$.$

$($a$)$

Assuming the kinetic coefficient of friction between steel and stone is $0\mathrm{.}30,$ calculate the angular acceleration $($in rad$/$s$2)$ of the grindstone. $($Indicate the direction with the sign of your answer.$)$

$($b$)$

How many turns $($in rev$)$ will the stone make before coming to rest?