Question

a train passes by a signal post in 30 seconds and 125 meters long bridge in 45 seconds find the length and speed of the train ?​

Answer 1

The correct answer is length of train is 250m and speed of the train is 8.33 m/sec.

Given: Time taken to pass signal post = 30 sec.

Length of bridge = 125m.

Time taken to cross bridge = 45 sec.

To Find: Length and speed of train.

Solution:

Let the speed of train = v

Let the length of train is = d

For passing signal post.

$Speed=\frac{Distance}{Time}$

v = $\frac{d}{30}$  (equation 1)

For crossing the bridge.

As we are crossing the bridge, the length of train and the length of bridge will be added.

v = $\frac{d+125}{45}$   (equation 2)

Equate equation 1 and 2 as both are the values of v.

$\frac{d}{30}=\frac{d+125}{45}$

45d = 30(d + 125)

45d = 30d + 3750

15d = 3750

d = 250m.

Put the value of d in equation 1.

v = $\frac{d}{30}$

v = $\frac{250}{30}$

v = $\frac{25}{3}=8.33$

Hence, length of train is 250m and speed of the train is 8.33 m/sec.

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