Two trains each 120 m long are moving in opposite directions.  They cross each other in 15 seconds. If the speed of one train is 30 km/h, find the speed of the other train.

27.6 km/hr

Total distance covered while crossing = 120 + 120 = 240 m

Time taken = 15 sec

Relative speed (S₁ + S₂) = \(\frac{Total\;Distance}{time}\) = \(\frac{240}{15}\) = \(\frac{48}{3}\) m/sec

                                     = \(\frac{48}{3}\) × \(\frac{18}{5}\) km/hr = 57.6 km/hr

Speed of one train = 30 km/hr (given)

Speed of other train = 57.6 - 30 = 27.6 km/hr