Question

A train 125 m long passes a man, running at 5 km/hr in the same direction in which the train is going, in 10 seconds. The speed of the train is

• A. $45$ km/hr
• B. $50$ km/hr
• C. $54$ km/hr
• D. $55$ km/hr

Answer 1

The correct option is B $50$ km/hr

Speed of the train relative to man $=\left(\frac{125}{10}\right)m/sec$
$=\left(\frac{25}{2}\right)m/sec$
$=(\frac{25}{2}\times \frac{18}{5})km/hr$
$=45km/hr$
Let the speed of the train be x km/hr. Then, relative speed = (x - 5) km/hr.
$\therefore x-5=45\Rightarrow x=50km/hr$.