Question 43373
As both the trains are moving in same direction, so the relative speed of the faster train with respect to the slower train = (50 - 32) = 18 km/hr.
As the man is sitting inside the slower train so, to him, the slower train is at rest and the faster train is moving at a speed of 18 km/hr.
The faster train passes the man in 15 seconds.
This means that the faster train travels a distance equal to its own length in 15 seconds, relative to the man inside the slower train.


Use this formula: {{{red(DISTANCE = SPEED x TIME)}}}.
To use this formula we have to use similar units for speed and time.
Here speed is in km/hr. We have to convert it to m/s.
{{{1 km/hr = (1000 m)/(3600 s) = 5/18}}} m/s
So 18 km/hr = {{{5*18/18}}} = 5 m/s
The distance traveled by the faster train in 15 seconds at a relative speed of 18 km/hr, as given by the formula, is 5 x 15 = 75 m


Hence, the length of the faster train is 75 m.