[填空题]
An automobile engine sb a4 f)/on /wsaqrc el1cw,l2,lows down from 4500 rpm to 1200 rpe,-w1hiea2ilt*v q i5m 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. $rev$