[填空题]
An automobile engine slows dow(w d p9il.qw 7w:wo.6cqp5zuvn from 4500 rpm to 1200 rpm in g6gd y4dd a*4s2.5 s. Calculate (a) its angular acceleration, assumed constant, $rad/s^2$ (b) the total number of revolutions the engine makes in this time. $rev$