Correct Answer - Option 3 : 900 m
Given:
Speed of train A = Speed of train B + 54 km/h
Time taken by train B to cross a man standing in train A = 1 minute
Formula:
Speed in km/h to m/s = multiply by 5/18
Distance = Speed × Time
Relative speed while going in the same direction = Difference of the speeds
1 minute = 60 seconds
Calculation:
Let speed of train B be x
So, speed of train A = x + 54
The difference in the speed of Train A and Train B = x + 54 – x = 54 km/h
54 km/h = 54 × 5/18 = 15 m/s
We know, relative speed = difference in the speed
Relative speed = 15 m/s
Time = 1 minute = 60 s
Distance = 15 × 60 = 900 m
∴ Length of the train B is 900 m