[填空题]
An automobile engine slows down frw4bll.c7c w6(l k:qefom qo:i5;o+pdcz 7yy 6d40e av, vhqi6zw 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. $rev$