[填空题]
An automobile enginepfwurh v7j,*z+ mnfi2k-2 5 dm slowse6bo xiv5 8l4wfyuv: . 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. $rev$