[填空题]
An automobile engine slows down from 4500 rm /-r5+ctlx1vpe*z6z mxy ; crpm zk( vqssrj0)*iij6gp6;v+ n)dd6ddfto 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. $rev$