A 100 m long train crosses a man travelling at `5 kmh^(-1)` , in opposite direction, in `7.2 s` then the velocity of train is

Options

A. 40 km/hr
B. 25 km/hr
C. 20 km/hr
D. 45 km/hr

Answer

D

Explanation

Length of train L=100m
Let speed of train `=v_(1)`
and speed of man `v_(m)=5 km//hr`
relative speed `=v_(1)+v_(m)`
`v_(rel)=("Separation")/("Time")=(100)/(7.2)m//s`
`=(1000)/(72)xx(18)/(5)=50 km//hr`
`therefore v_(1)+5=50 rArr v_(1)=45 km//hr`