Question

The diameter of the wheels of a bus is 140 cm. How many revolutions per minute do the wheels make when the bus is moving at a speed of 72.6 km per hour?

Answer 1

Diameter of the wheel = 140 cm
Radius = 70 cm
Circumference = $2\mathrm{\pi r}$
$$\begin{gathered} =2\times \frac{22}{7}\times 70 \\ =440\mathrm{cm} \end{gathered}$$
Speed of the wheel = 72.6 km per hour
Distance covered by the wheel in 1 minute = $\frac{72.6\times 1000\times 100}{60}$ = 121000 cm
​Number of revolutions made by the wheel in 1 minute =$\frac{\mathrm{Total}\mathrm{distance}\mathrm{covered}}{\mathrm{Circumference}}$

$$\begin{gathered} =\frac{121000}{440} \\ =275 \end{gathered}$$

Hence, the wheel makes 275 revolutions per minute.