$.)$ You have a grindstone $($a disk$)$ that is $90\mathrm{.}0$kg$,$ has a $0\mathrm{.}340$m radius, and is turning at $0\mathrm{.}0$ rpm$,$ and you press a steel axe against it with a radial force of $20\mathrm{.}0$N$.($a$)$ assuming the kinetic coefficient of friction between steel and stone is $0\mathrm{.}20$ calculate the angular acceleration of the grindstone. $($b$)$ How many turns will the stone make before coming to rest?