Question

How long will a boy sitting near the window of a train travelling at 54 km/h see a train passing by in the opposite direction with a speed of 36 km/hr ? The length of the slow moving train is 100 m.

Answer 1

Speed is converted to m/s

$54\times 5/18=15m/s36\times 5/18=10m/s$

the relative speed of two approaching bodies is the sum of the two speeds.

Relative speed:

$15+10=25m/s$

Relative distance $=100m$

Time$=distance/speed$

$=\frac{100}{25}$

$=4second$