A train A which is 120 m long is running with velocity 20 m/s while train B which is 130 m long is running in opposite direction with velocity 30 m/s. What is the time taken by train B to cross the train A?

Options

A. 5 s
B. 25 s
C. 10 s
D. 100 s

Answer

A

Explanation

Length of train A = 120 m
Velocity of train A , `v_A` = 20 m/s
Length of train B = 130 m
Velocity of train B, `v_B` = 30 m/s
Relative velocity of B w.r.t A = `v_B + v_A` = 50 m/s
(trains move in opposite directions)
Total path length to be covered by B = 130 + 120 = 250 m
`therefore` Time taken by train B = 250 m/50 m/s = 5 s