Two trains go towards each other at speeds, modules of which are 54 km / h and 36 km / h. The length of the second

Two trains go towards each other at speeds, modules of which are 54 km / h and 36 km / h. The length of the second train is 250 meters. How long will a passenger sitting on the first train see an oncoming train passing by?

Since the trains are moving towards each other, the speed of the second train relative to the first will be equal to the sum of their speeds:

54 + 36 = 90 km / h.

Since the length of the first train is 250 m (1/4 km), the time during which the passenger will observe the second train will be:

1/4: 90 = 1/360 hours = 1/6 minutes = 10 seconds.

Answer: the required time is 10 s.