[填空题]
An automobile engine slows down from 4500 rpm 0t4vqnpr x b .j:r+xp;to 1200 rpm in 4i0 /9+lw6 1vuxhgcm ks- iujugl9 0lj2.5 s. Calculate (a) its angular acceleration, assumed constant, $rad/s^2$ (b) the total number of revolutions the engine makes in this time. $rev$