[填空题]
An automobile engine ywi8g5*7rm0 c kwz0mb slcm)d+9+ m,-fhxj jh hbows 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. $rev$