Question:
Find the length of the arc of a circle of diameter 42 cm which subtends an angle of 60° at the centre.
Solution:
We have $r=\frac{\text { diameter }}{2}=\frac{42}{2}=21 \mathrm{~cm}$ and $\theta=60^{\circ}$
Length of arc $=\frac{\theta}{360^{\circ}} \times 2 \pi r=\frac{60^{\circ}}{360^{\circ}} \times 2 \times \frac{22}{7} \times 21=22 \mathrm{~cm}$
Hence, the length of the arc of the circle is 22 cm.