You have a grindstone $($a disk$)$ that is $90\mathrm{.}0$kg$,$ has a $0\mathrm{.}340-$m radius, and is turning at $90\mathrm{.}0$ 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 $($in rad s$^2)$ of the grindstone. $($Indicate the direction with the sign of your answer.$)$ rad $/$ s$^2($b$)$ How many turns $($in rev$)$ will the stone make before coming to rest? $$ rev