Question
A train of length (L + 50) meters crosses a man running in
the same direction in 25 seconds. The same train crosses a bridge of length (L - 100) meters in 30 seconds. If the speed of the man is 18 kmph, then find the value of 'L'.Solution
Let the speed of the train be 'S' m/s,
Speed of the man = 18 kmph = 5 m/s
Length of the train = (L + 50) metres
ATQ,
L + 50 = (S - 5) X 25
L = 25S - 175 --- (i)
Sum of the length of Train and bridge = L + 50 + L – 100 = (2L - 50) metres
Now,
2L - 50 = 30S
Using value of 'L' from equation (i), we get:
2 X (25S - 175) - 50 = 30S
Or, 50S - 350 - 50 = 30S
Or, 20S = 400
So, 'S' = 20
Required value of 'L' = 25 X 20 - 175 = 325
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