The two trains are moving towards each other at speeds of 36 km / h and 54 km / h.

The two trains are moving towards each other at speeds of 36 km / h and 54 km / h. The length of the first train is 40 m, the second 50 m. Trains will pass each other during the current.

v1 = 36 kilometers / hour = 10 meters / second – the speed of the first train;

v2 = 54 kilometers / hour = 15 meters / second – the speed of the second train;

L1 = 40 meters – the length of the first train;

L2 = 50 meters – the length of the second train.

It is required to determine t (seconds) – the time interval during which the trains will pass each other.

According to the condition of the problem, the trains are moving towards each other. Then, their relative speed of movement will be equal to:

v = v1 + v2 = 10 + 15 = 25 meters / second.

The total distance that the train must travel will be equal to:

L = L1 + L2 = 40 + 50 = 90 meters.

Then the time will be:

t = L / v = 90/25 = 3.6 seconds.

Answer: trains will pass each other for a period of 3.6 seconds.