Question

A train moves past a telegraph post and a bridge $264$ m long in $8$ seconds and $20$ seconds respectively. What is the speed of the train in km/hr?

• A. $78.2$ km/hr
• B. $71.2$ km/hr
• C. $73.2$ km/hr
• D. None of these

Answer 1

The correct option is D None of these

Let the length of the train be $x$ m.

Distance covered is $264$ m

Total time taken to cross the bridge is 20 sec.

Speed is $\frac{x+264}{20}$ m/sec

The speed of the train when it passes a post is $\frac{x}{8}$m/sec.

Equating both speeds,

$\frac{x}{8}=\frac{x+264}{20}20x=8x+211212x=2112x=176m$

So, the speed of the train is $22$m/sec.

Converting to km/hr, we get the speed as $79.2$km/hr.

Hence option D.