[填空题]
An automobile engine slow.5;q.haboe g cs down4go;cg4 )ry9 8 a ej,lrshnj2d 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. $rev$