Question

A boy is cycling such that the wheels of the cycle are making $140$ revolutions per minute. If the diameter of the wheel is $60cm$, calculate the speed per hour with which the boy is cycling.

Answer 1

Given the diameter of wheel$=60cm$

Radius of wheel $=\frac{60}{2}=30cm$
Circumference of wheel$=2\mathrm{\pi r}$
$$\begin{gathered} =2\times \mathrm{\pi }\times 30 \\ =2\times \frac{22}{7}\times 30 \\ =\frac{1320}{7} \end{gathered}$$

Distance covered in $140$ revolution:
$$\begin{gathered} =140\times \frac{1320}{7}cm \\ =26400cm \\ =264m \\ =\frac{264}{1000}km \end{gathered}$$

Thus, distance covered in $1hour=\left(\frac{264}{1000}\right)\times 60$.

Speed $=\frac{Dis\tan ce}{time}=\frac{{\displaystyle \frac{264\times 60}{1000}}}{1}=\frac{264\times 60}{1000}=15.84km/hr$

Hence, the speed per hour with which the boy is cycling is $15.84km/hr$.