Two trains which are 180 m and 170 m in length are running towards each other on the parallel lines at a speed of 72 km/hr and 54 km/hr res…

Since the trains are travelling towards each other, we have

Relative speed = 72 + 54 = 126 kmph

Converting it into m/s, we have

126 kmph = 126 × 5/18 = 35 m/s

Time taken to cross each other = (180 + 170)/35 = 10 sec