Question

If the wheel of the bus with 90 cm diameter makes 210 revolutions per minute. Find the speed of bus in km/hr.

Answer 1

Diameter of the wheel = 90 cm
Circumference of the wheel = $\pi$ × diameter
= 3.14 × 90 cm
= 282.6 cm

= $\frac{282.6}{100}\mathrm{m}$

= $\frac{282.6}{100000}\mathrm{km}$

= 0.002826 km

It is given that it takes 210 revolutions in 1 min.

Number of revolutions taken by the wheel in 1 h = 210 × 60 = 12600

$$\begin{gathered} \mathrm{Now},\mathrm{no}.\mathrm{of}\mathrm{revolutions}=\frac{\mathrm{total}\mathrm{distance}}{\mathrm{circumference}\mathrm{of}\mathrm{the}\mathrm{wheel}} \\ \Rightarrow 12600=\frac{\mathrm{total}\mathrm{distance}}{0.002826} \\ \Rightarrow \mathrm{Total}\mathrm{distance}=12600\times 0.002826=35.61\mathrm{km} \end{gathered}$$

The distance covered in 1 h is equal to the speed of the bus.
∴ Speed of the bus = 35.61 km/h