[填空题]
An automobile engine slows down frz *bf3.t)tc cmwds2em9 py53hom 9a,+lg5,cb*jcdzsl n4500 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. $rev$