# Two trains A and B of length 400m each are moving on two parallel tracks with a uniform speed of 72km/h in the same direction, with A ahead of B. The driver of B decides to overtake A and accelerates by 1m/s. If after 50s, the guard of B just brushes past the driver of A, what is the original distance between them?

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Two trains A and B of length 400m each are moving on two parallel tracks with a uniform speed of 72km/h in the same direction, with A ahead of B. The driver of B decides to overtake A and accelerates by 1m/s. If after 50s, the guard of B just brushes past the driver of A, what is the original distance between them?

(a) 50m

(b) 150m

(c) 125m

(d) 1250m

I got this question at a job interview.

Question is from Acceleration due to Gravity in chapter Laws of Motion of Engineering Physics I

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The correct choice is (d) 1250m

The explanation is: Let x be the distance between then driver of train A and the guard of train B. Initially, both trains are moving in the same direction with the same speed of 72km/h. So relative velocity of B with respect to A = vB-vA = 0. Hence the train B needs to cover a distance with a= 1m/s, t = 50 s, u = 0

s = ut + 1/2at^2 = 1250m.

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