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Discussion :: Problems on Trains

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

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

Explanation :

Let the length of the first train be x metres.

Then, the length of the second train is $$(\frac { X} { 2 } ) metres$$

Relative speed = (48 + 42) kmph = $$(90\times\frac{5}{18})m/sec = 25m/sec$$

$$\frac{(X +\frac{X}{2})}{25}=12$$  or $$(\frac { 3X } { 2 } ) =300$$ or  X=200

Let the length of platform be y metres. Length of first train = 200 m.

Speed of the first train = $$(48\times\frac{5}{18})m/sec$$ = $$(\frac { 40 } { 3 } ) m/sec$$

$$((200+y)\times\frac{3}{40})$$ =45

600 + 3y = 1800

y = 400 m.

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