A train 180 metres long crosses a stationary pole in 9 seconds. What is its speed in kilometres per hour?

हल

1. 01

   To pass a pole, the train must travel its own length, so the distance is 180 metres.

2. 02

   Speed is $\frac{180}{9} = 20$ metres per second.

3. 03

   Convert with $1\ \text{m/s} = \frac{18}{5}\ \text{km/h}$: $20 \times \frac{18}{5} = 72$ km/h.