Question

A man is standing on a railway bridge which is 180 m long. He finds that a

train crosses the bridge in 20 seconds but himself in 8 seconds. Find the length of

the train and its speed in kmph?​

Answer 1

Consider the man as a point. Let l and v be the trains length and velocity. Then:

8v=1

20v=l+180

12v=180

v=180/12=15 m/s

15 m/s x 8 s=120m as the length of the train

Answer 2

The length of train is 120 m and speed is 54 km/hr.

Step-by-step explanation:

Let the length of train be 'x'.

Length of bridge = 180 m

Time a train crosses the bridge = 20 sec

Time a train crosses a man = 8 sec

So, According to question, it becomes,

$\dfrac{Distance}{Time}=Speed\\\\\dfrac{x}{8}=s$

Similarly,

$\dfrac{x+180}{20}=s$

So, equating both the equations we get that

$\dfrac{x}{8}=\dfrac{x+180}{20}\\\\20x=8(x+180)\\\\20x=8x+1440\\\\20x-8x=1440\\\\12x=1440\\\\x=120$

So, the speed would be

$\dfrac{120}{8}=15\ m/s=15\times \dfrac{18}{5}=3\times 18=54\ km/hr$

Hence, the length of train is 120 m and speed is 54 km/hr.

# learn more:

A man standing on a railway bridge which is 180 m long . He find that a train crosses that bridge in 20 seconds but himself in 8 seconds. Find the speed of the train?

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