[填空题]
An automobile engine slows down frovlxd;a0 6b po, xqn3c(m 450e3; h6n nutmt0ypc2dpp.i k4;0 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. $rev$