Question

 A train M 315 metres long, running at speed of 60 km/hr crosses another train N in 21 seconds, which is running at speed of 54 km/hr in the opposite direction of M. What is the length of the train N?
1. 560 m
2. 350 m
3. 450 m
4. 250 m

Answer 1

Correct Answer - Option 2 : 350 m

Given,

Length of train M, a = 315 metres

Speed of train M = 60 km/hr

Speed of N = 54 km/hr

Time is taken to cross each other, t = 21 seconds

Formula used:

Relative Speed = (Sum of the lengths of trains)/(Time taken to cross each other)

Calculation

Let the length of train B is b metres

If trains are running in the opposite direction,

Relative speed = (60 + 54) km/hr

= 114 km/hr

= 114 × (5/18) m/sec

= (95/3) m/sec

Relative speed = sum of the lengths of trains/time taken to cross each other

⇒ 95/3 = (a + b) / t

⇒ 95/3 = (315 + b) / 21

⇒ (95/3) × 21 = 315 + b

⇒ 665 = 315 + b

⇒ b = 665-315

⇒ b = 350 metres

∴ Length of the train N = 350 metres