Two trains moving in the same direction, and running respectively at 72km/h and 144km/h cross each other in 5sec. What is the length of each train if the two trains are equally long?
The trains cover a distance equal to the sum of their lengths at a relative speed 144 - 72 = 72km/h × (5/18), or 20m/s. We can use the speed distance formula: sum of lengths = 20 × 5 = 100m. Halving this we get the length of one train = 50m.