Question

A train travelling at 48 km/h completely crosses another train having half the length of first train and travelling in opposite direction at 42 km/h in 12 seconds. The train having speed 48 km/h also passes a railway platform in 45 seconds. What is the length of the platform ?

Accepted Answer

C. Let length of 1st train be $x$ m. Length of 2nd train = $0.5x$ m. Relative speed = $48 + 42 = 90$ km/h = $90 	imes \frac{5}{18} = 25$ m/s. Distance covered = $x + 0.5x = 1.5x$. $1.5x = 25 	imes 12 = 300 \implies x = 200$ m. Now, speed of 1st train = $48$ km/h = $48 	imes \frac{5}{18} = \frac{40}{3}$ m/s. Passing platform of length $L$ in 45 s: $\frac{200 + L}{40/3} = 45 \implies 200 + L = 45 	imes \frac{40}{3} = 600 \implies L = 400$ m. Hence, Option C is correct.

Trains and Platform Length

Explanation

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