A train 100 m long meets a man going in opposite direction at 5 km/h and passes him in $7\frac{1}{5}$ sec. The speed of the train is

A) 40 km/hr

B) 45 km/hr

C) 50 km/hr

D) 55 km/hr

E) 56 km/hr


Option B


Let speed of the train be $x$ km/hr

Relative speed of the train with respect to man $=x+5$ km/hr

Time taken $=\frac{36}{5}$ sec $=\frac{36}{(5\times 60\times 60)}$ hr

Speed $=\frac{Distance }{Time}$

$x+5$ $=\left(\frac{100 }{1000}\times\frac{5\times 60\times 60}{36}\right)$

$\Leftrightarrow x=50-5$ = 45km/hr