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 150 m. The magnitude of the difference in the speeds of the two trains (in m/sm/s) is ____2 m/s________.
speed=150/15 - 120/10 =|10 -12|=2 m/s