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Q: 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 ?

  • 1
    250 mts
  • 2
    400 mts
  • 3
    320 mts
  • 4
    390 mts
  • Show Answer
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Answer : 2. "400 mts"
Explanation :

Answer: B) 400 mts 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.

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