A dentist's drill starts from rest. After $3\mathrm{.}20$ s of constant angular acceleration it turns at a rate of $2\mathrm{.}5110^4$rev $/$ min. $($a$)$ Find the drill's angular acceleration. rad $/$ s$^2($b$)$ Determine the angle $($in radians$)$ through which the drill rotates during this period. rad