Question

A man standing on a railway bridge which is 180m long .He finds that a train crosses the bridge in 20s but himself in 8 sec. Find the length of train and its speed

Answer 1

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 45kmph

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