Question

The wheels of the locomotive of a train are 2.1 m in radius. They make 75 revolutions in one minute.

Answer 1

Radius of the wheel = 2.1 m
Circumference of the wheel = $2\mathrm{\pi r}$
$$\begin{gathered} =2\times \frac{22}{7}\times 2.1 \\ =13.2\mathrm{m} \end{gathered}$$
Distance covered by the wheel in 1 revolution = 13.2 m
Distance covered by the wheel in 75 revolutions = $(13.2\times 75)=\left(990\times \frac{1}{100}\right)\mathrm{m}$
$=\left(990\times \frac{1}{1000}\right)\mathrm{km}$
Distance covered by the wheel in 1 minute = Distance covered by the wheel in 75 revolutions =$\frac{990}{1000}$ km

∴ Distance covered by the wheel in 1 hour = $\frac{990}{1000}\times 60$
= $59.4\mathrm{km}/\mathrm{h}$