Question

A 100m. crosses a person travelling at 5km/h in 7.2sec . Find the velocity of the train?

Answer 1

Hello!

• Let the speed of the train be x kmh⁻¹

Since,
The man and the train are moving in opposite direction :-

$\textbf{The \:relative \:speed}$ = $\boxed{\sf (5 + x) \:kmh^{-1}}$

• Time taken to overtake the man :-

100 m = 0.1 km in 7.2 seconds = 7.2 / 3600 = $\boxed{\sf 0.002\: hours}$

Then,

Time = $\dfrac{\sf Distance} {\sf Speed}$

Time = $\dfrac{\sf 0.1}{\sf x + 5} = \sf 0.002$

x + 5 = $\dfrac{\sf 0.1}{\sf 0.002} = \sf 50$ ⇒ $\boxed{\sf x = \sf 45}$

Hence,
The speed of the train is 45 kmh⁻¹

Cheers!