The speed of train A and train B is 93 km/hr and 51km/hr, respectively. When both the trains are running in the opposite direction, they cross each other in 18 seconds. The length of train B is half of the length of train A. If train A crosses a bridge in 42 seconds, then find the length of the bridge.
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610 m
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480 m
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605 m
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240 m
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485 m
C
Correct answer
Explanation
Relative speed when moving opposite = 93 + 51 = 144 km/hr = 144 × (5/18) = 40 m/s. Total length (A + B) = 40 × 18 = 720 m. Let length of A = L, so B = L/2. Then L + L/2 = 720, giving L = 480 m. Length of B = 240 m. Train A crossing bridge at 93 km/hr = 93 × (5/18) = 155/6 m/s. Time = 42 sec, so distance covered = (155/6) × 42 = 1085 m. Bridge length = 1085 - 480 = 605 m.