[填空题]
An automobile engine sg q2n* vp4kiul.9 pkj()n1yif7eno f. m2csw 3e4dygfw/co14w 4yw5mq iy u;5lows 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. $rev$