[填空题]
An automobile engine slows down from 45y5bi0maom3ap6 z5 j/sn.ek2 t0g bsxng )b3h9yp 4u,o0 opor,v)2g8gd0 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. $rev$