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
69.5 km/hr
70 km/hr
79 km/hr
79.2 km/hr
Explanation:
Let the length of the train be $ x $ metres and its speed by $ y $ m/sec.
Then,$ \dfrac{x}{y} $= 8 $\Rightarrow x = 8 y $ |
Now,$ \dfrac{x + 264}{20} $= $ y $ |
$\Rightarrow 8 y $ + 264 = 20$ y $
$\Rightarrow y $ = 22.
$\therefore Speed = 22 m/sec$ =$ \left(22 \times\dfrac{18}{5} \right) $km/hr = 79.2 km/hr. |