Question

Two trains A and B of length 400 m each are moving on two parallel tracks with a uniform speed of 72 im/h in the same direction, with A ahead of B. The driver of B decides to over take A and accelerates by 1 m/s2 .If after 50s the guard of B just brushes past the drives of A, what was the original distance between them?

Answer 1

hint 1: consider the distance from back of train A and front of train B as x.

hint 2: u=72, a=1, t=50, S=x

hint 3(solution): use formula  s=ut+1/2at2

Answer 2

For train A,

The u, initial velocity = 72 km/h = 20 m/s

t, time = 50 sec

acceleration, a1 = 0 = due to uniform velocity

distance covered by A, s = ut + ½ at^2

s = 20 * 50 + ½ * 0 * 50^2 = 1000 m

For train B,

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

a2 accenleration = 1 m/s^-2

time t = 50 s

distance covered, s = ut + ½ at^2

s = 20 * 50 + ½ * 1 * 50^2

2250 m

Length = 2 * 400 m = 800 m