[填空题]
A new high-speed 12-car Italian train ha1p )sxb v:srh/h 4hcj/s a mass of 660 metrz3d*xl5za 1 /tbk swq*ic 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.