It takes 10 s and 15 s, respectively, for two trains travelling at different constant speeds to completely pass a telegraph post. The length of the first train is 120 m and that of the second train is
Speed of the first train = length/time = 120/10 = 12m/s Speed of the second train = length/time = 150/15 = 10m/s 2.0 m/s is the difference in the train speed.