Question

A train travelling at 48 km per hr crosses another train having half it's its length and travelling in opposite direction at 42 km per hour in 12 second it also pass is a railway platform in 45 seconds the length of platform is ???

Answer 1

let x and y represent the longer and the shorter train respectively

speed of x = 48 km/h
speed of y = 42 km/h
time taken for x to cross y = 12 s
length of the longer train = relative speed of x and y × time
= (48 km/h - 42 km/h) × 12 s
= 6 km/h × 12 s
= 6 km/h × 12 / 3600 h
= 0.02 km
= 20 m
and length of y = 1/2 × length of x
= 1/2 × 20 m
= 10 m

now,
length of platform = 42 km/h × 12 s
= 48 km/h × 45/3600 h
= 0.6 km
= 600 m