Question

A train traveling at 48 kmph completely crosses another train having half its length and traveling in opposite direction at 42 kmph, in 12 seconds. It also passes a railway platform in 45 seconds. The length of the platform is

• A. 560 m
• B. 400 m
• C. 600 m
• D. 450 m

Answer 1

The correct option is B 400 m

$\text{Let the length of first train be}x\text{metres.}\text{Then, the length of second train is}\left(x/2\right)\text{metres.}\text{Relative speed}=(48+42)kmph=(90\times \frac{5}{18})m/sec=25m/sec.\therefore \frac{(x+\frac{x}{2})}{25}=12or\frac{3x}{2}=300orx=200.\therefore \text{Length of first train}=200m.\text{Let the length of platform be}y\text{metres.}\text{Speed of the first train}=(48\times \frac{5}{18})m/sec=\frac{40}{3}m/sec.\therefore (200+y)\times \frac{3}{40}=45\Rightarrow 600+3y=1800\Rightarrow y=400m$