Question

The radius of the wheel of a vehicle is 42 cm. How many revolutions will it complete in a 19.8-km-long journey?

Answer 1

Radius of the wheel = 42 cm
​Circumference of the wheel = $2\mathrm{\pi r}$
$$\begin{gathered} =2\times \frac{22}{7}\times 42 \\ =264\mathrm{cm} \\ =\frac{264}{100}\mathrm{m} \\ =2.64\mathrm{m} \end{gathered}$$

Distance covered by the wheel in 1 revolution = 2.64 m

Total distance = 19.8 km or 19800 m

∴ Number of revolutions taken by the wheel = $\frac{19800}{2.64}=7500$