以迎面而来的列车为参照物,乘客的列车速度为:v=15m/s+20m/s=35m/s
(1)S1=140m,t1=S1/v=140m/35m/s=4s
(2)S2=140m+120m=260m,t2=S2/v=260m/35m/s=7.43s