Question

A person is standing on a railway bridge which is 180 m long. A train crosses that person in 8 sec and the bridge in 20 sec. Find the speed and length of the train ?

Answer 1

Explanation:

Asume L is the length of the train and S is the Speed

Speed of the train will be S = (180+L)/20

Assuming that S is constant, and knowing that the train takes 8 sec to pass a single point (the man), then:

S = L / 8

We now have two different ways of deriving S, both of which use L. So we can say that

(180 + L) / 20 = L / 8. Solving this L is 120. Substitute this in any one of the equation S will 15mps.

Let the length of the train be x meters Then, the train covers x meters in 8 seconds and (x + 180) meters in 20 seconds. Therefore x/8 = (x+180)/20 20x = 8(x+180) x = 120 Therefore Length of the train = 120m Speed of the train = 120/8 m/sec = 15 m/sec =15 * 18/5 kmph = 54kmph

ans: 120m and 54km/h

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