Question

How long will a boy sitting near the window of a train travelling at 54 km/hr see a train passing by in the opposite direction with a speed of 36 km/hr. the length of the slow-moving train is 100m?

Answer 1

Given:

Speed of train where boy is sitting, v= 36 km/h =10 m/s

Speed of train observed by boy, u = 18 km/h = 5 m/s

Length of train, l= 100 m

To find:

Time of passing train, t=?

Formula used:

Speed = $\frac{ distance }{time}$

Solution:

The speed of the train is given by,

Speed = $\frac{ distance }{time}$

Time = $\frac{ distance }{velocity}$

Here, distance = length of train

Velocity = relative velocity of two trains

Thus, Time= $\frac{ length }{ relative velocity}$

relative velocity

= v-(-u)

= 10- (-5)

=15 m/s

Time= $\frac{ 100 }{15}$

t=6.667 second

Thus, the boy will see train passing for 6.667 second.