A train travelling at 48 kmph crosses another train having half its length and travelling in opposit...........

Quant (SSC) Problems on trains

A train travelling at 48 kmph crosses another train, having half its length and travelling in opposite direction at 42 kmph, in 12 sec. It also covers a bridge in 45 sec. Find the length of the bridge ?

250 mts

400 mts

320 mts

390 mts

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Explanation:

Explanation:
Let the length of the 1st train = L mts
Speed of 1st train = 48 kmph
Now the length of the 2nd train = L/2 mts
Speed of 2nd train = 42 kmph
Let the length of the bridge = D mts
Distance = L + L/2 = 3L/2
Relative speed = 48 + 42 = 90 kmph = 90 x 5/18 = 25 m/s(opposite)
Time = 12 sec
=> 3L/2x25 = 12
=> L = 200 mts
Now it covers the bridge in 45 sec
=> distance = D + 200
Time = 45 sec
Speed = 48 x5/18 = 40/3 m/s
=> D + 200/(40/3) = 45
=> D = 600 - 200 = 400 mts
Hence, the length of the bridge = 400 mts.