Question

Two trains left Delhi to Agra at an interval of 10 minutes and each with a speed of 30 km/hr. What was the speed of a third train moving towards Delhi, if it met these two trains at an interval of 4 minutes?
a) 30 km/h
b) 45 km/h
c) 15 km/h
d) 20 km/h

Answer 1

The answer is 30km/h

Answer 2

Answer:

The velocity of third train is 45 km/h

B is correct

Explanation:

Two trains left Delhi to Agra at an interval of 10 minutes and each with a speed of 30 km/hr.

First we find the distance of two train leave from Delhi to Agra

$\text{Distance }=\text{Speed}\times \text{Time}$

Distance of two trains = $30\times \dfrac{4}{60}=5$ km

if third train met these two trains at an interval of 4 minutes.

This 5 km distance covered in 4 minutes.

One train running towards third train.

Relative velocity of two train.

Let speed of third train be v

$30+v=\dfrac{5}{4}\times 60$

$30+v=75$

$v=45\text{km/h}$

Hence, The velocity of third train is 45 km/h