Question

A train has a speed of 5m/s while a bird has a speed of 10m/s. It takes 80 secs for the bird to fly from the back of the train to the front, and back again. How long is the train?

Answer 1

The length of the train is `=300m`

Explanation:

Let the length of the train `=Lm`

The bird flying in the same direction of the train

The relative velocity of the bird wrt the train is

`v=10-5=5ms^-1`

The time taken to fly from the back to the front is

`t_1=L/5`

The bird flying in the opposite direction of the train

The relative velocity of the bird wrt the train is

`v=10-(-5)=15ms^-1`

The time taken to fly from the front to the back is

`t_1=L/15`

`t_1+t_2=80`

`L/5+L/15=80`

`L(1/5+1/15)=L*4/15=80`

`L=15*80/4=300m`