Question

How long will a man take to make a round of a circular field of radius $21m$, cycling at the speed of $8km/h$?

Answer 1

Radius of the circular field, $\left(r\right)=21m$.
Distance covered by the cyclist $=$ Circumference of the circular field

Circumference of the circular field $=2\pi r$

$=2\times \frac{22}{7}\times 21m$

$=2\times 22\times 3cm$

$=132m$

$\Rightarrow$ Circumference of the circular field $=132m$.----(1)

Speed of the cyclist $=8km/h$

$=8\times \frac{1000m}{3600s}$ [Since, $1km=1000m,1hour=3600seconds$]

$=\frac{20m}{9s}$

Speed of the cyclist $=\frac{20m}{9s}$---(2)

Time taken by the cyclist to cover the field $=\frac{\text{Distance covered by cyclist}}{\text{Speed of the cyclist}}$

$=\frac{132m}{\frac{20m}{9s}}$

$=132\times \frac{9}{20}s$

$=6.6\times 9s$

$=59.4s$

Therefore, Time taken by cyclist to to make a round of a circular field is $59.4$ seconds.