Discussion of Question with ID = 018 under Problems-on-Trains

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Question

Two equally long trains of length 90m cross each other in 6sec. If one train is twice as fast as the other, then what is the speed of the faster train?

A

72 km/h.

B

73 km/h.

C

71 km/h.

D

74 km/h.

Soln.
Ans: a

Let the speeds be v and 2v. The trains cover a distance equal to the sum of their lengths at a relative speed v + 2v = 3v. We can use the speed distance formula: $3v = {90 + 90}/6$, which gives v = ${180/{3 × 6}} × (18/5)$ = 36km/h. So the speed of the faster train is twice = 72km/h.


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