Train A crosses train B completely in 90 seconds, with the trains running in opposite directions. The lengths of the trains A and B are 900 metres and 1800 metres. respectively. If the speed of train A is 45 km/h, then in how much time can train B cross a stationary pole?
Answer & explanation
Correct answer: option 3
Let speed of train B = S km/h
Relative speed ( when both moves in same direction ) = ( S + 45 ) km/h
Distance = ( 900 + 1800 ) = 2700 m
We know ,
Speed = \(\frac{Distnace}{Time}\)
= \(\frac{2700}{90}\) = 30 m/sec
30 m/sec = 30 × \(\frac{18}{5}\) km/h = 108 km/h
( S + 45 ) km/h= 108 km/h
S = 63 km/h = \(\frac{35}{2}\) m/sec
Time taken by train B to cross pole = \(\frac{1800×2 }{35}\)
= \(\frac{720 }{7}\) sec