[填空题]
An automobile engine slows down from 4500 rpb k0pjdli3 qh4j;mg, 5m to 1200 4 eoqh4papsx 4g7sk5bm;8fp0 rpm in 2.5 s. Calculate (a) its angular acceleration, assumed constant, $rad/s^2$ (b) the total number of revolutions the engine makes in this time. $rev$