Two trains A and B of length 400 m each are moving on two parallel tracks with a uniform speed of 72 km h–1 in the same direction, with A ahead of B. The driver of B decides to overtake A and accelerates by 1 m s–2. If after 50 s, the guard of B just brushes past the driver of A, what was the original distance between them ?

In case of train A:

Initial velocity, *u* = 72 km/h = 20 m/s

Time, *t* = 50 s

Since the train is moving with uniform velocity,

Acceleration, *a*_{I} = 0

Now, using second equation of motion,

Distance covered by train A is given by,

For train B,

Initial velocity, u_{B} = 72 km/h = 20 m/s

Acceleration, *a* = 1 m/s^{2 }

Time,* t* = 50 s

Now, using second equation of motion,

Distance travelled by second train B is,

Length of both trains = 2

Therefore, the original distance between the driver of train A and the guard of train B = 2250 - 1000 - 800

= 450m.

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