[填空题]
An automobile enginez 6i;ddmx :q(i :y3l9b ep74 .1xbqgb+hhwuaaslows 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. $rev$