[填空题]
An automobile engine slows down from 4500 rpm u. 43drw;hdp nmqn37u scz +xpxec.w 0nvc653to 1200 rpm ind/d,+fkea.u 9x 3 n2ar q)mfrc 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. $rev$