Question

Two identical train take 3 second to pass one another when going in opposite direction.But take only 2.5 second,if the speed of one is increased by 50%. The time one would take to pass the other when going in same direction at their original speed is-(both train is moving with constant velocity)

Answer 1

let train A is moving along positie x axis with vel = +V

train B along negative x axis = -U

vel of train A with respect B is = V-(-U) = V+U

let S be distance

S=(V+U)3

S=(V + U + U/2)2.5

=> S= (V+3/2U)2.5

get v and u in terms of S

then apply S=(V-U)t    (now V along and u in same direction v=V-U)

and find t

may be answer 30/4 secs