Question

A train of length 126 m moves with a certain velocity . Another train of same length moving with the velocity twice that of first train. Time of crossing between them is 3 seconds.Find the individual velocities of the train.

Answer 1

Let v1 be the velocity of the first train and v2 be the velocity of the second train. Then, v2 = 2v1.

Distance covered at the time of crossing the trains = 126m
Time taken = 3 seconds.

Also, when two trains travelling in opposite directions cross each other, the apparent speed of the two trains is v1-(-v2) = v1+v2.

Since v2 = 2v1, the apparent speed of the two trains would be 3v1.

We also know that velocity = distance / time.

Here, distance covered is 126m, since the length of the train is 126m, and time taken is 3 seconds.

Apparent velocity = 3v1 = 126/3

or v1 = 126/9 = 14m/s and v2 = 2 x 14 m/s = 28m/s.

This, the first and second trains are travelling at 14m/s and 28m/s respectively.