A man standing on a platform finds that a train takes 3 seconds to pass him and another train of the same length moving in the opposite direction, takes 4 seconds. The time taken by the trains to pass each other will be
Solution
Let the length of both the trains = l metre(equal) speed of the first train = s1 m/s
and another's speed= s2 m/s
ATQ,
$\dfrac{l}{s1} = 3$
$sl = \dfrac{l}{3} ………1$
Again
$\dfrac{l}{s2} = 4$
$s2 = \dfrac{l}{4} …….2$
Crossing time in opposite direction to each other.
$= \dfrac{total ~distance}{total~speed} = \dfrac{l + l}{\dfrac{l}{3} + \dfrac{l}{4}} = \dfrac{2l}{7l} \times 12$
$= \dfrac{24}{7}$ sec
$= 3\dfrac{3}{7}$ sec