[填空题]
A new high-speed 12-car Itali p5ke9. q wo dvyam-7+-,q1i wqrrz9rean train has a mass of 660 metriczm hwgd g kb(awg31648 tons (660,000 $\mathrm{~kg}$) . It can exert a maximum force of 400 kN horizontally against the tracks, whereas at maximum velocity ( 300 $\mathrm{~km} / \mathrm{h}$) , it exerts a force of about 150 kN . Calculate (a) its maximum acceleration
(b) estimate the force of air resistance at top speed.
