[填空题]
An automobile engine afs7scu/ of5,y0b m; zasm8y 69ov/4uroy 9ei ulmfbt 7+) (:a7tjcycslows down from 4500 rpm to 1200 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. $rev$