Two trains are moving in the same direction and take 1 minute 12 seconds to completely cross each other. The speeds of Train A and Train B are 90 km/h and 72 km/h respectively. If Train A is 40 metres longer than Train B, find the length of Train
A.

ATQ,
Since both trains are moving in the same direction, relative speed will be the difference of their speeds.
Relative speed = 90 − 72 = 18 km/h
Convert 18 km/h into m/s:
18 km/h = (18 × 5/18) m/s = 5 m/s
Time taken to cross each other = 1 minute 12 seconds = 72 seconds
Distance covered while crossing = Relative speed × Time
= 5 × 72
= 360 metres
This distance is equal to the sum of the lengths of both trains.
Let the length of Train B be x metres.
Then the length of Train A = x + 40 metres.
So,
x + (x + 40) = 360
2x + 40 = 360
2x = 320
x = 160
Length of Train A = 160 + 40 = 200 metres