Question

Find the perimeter and area of semicircles(Half cut rings) whose diameters are
i) $2.8$ cm
ii) $56$ cm
iii) $84$ cm
iv) $112$ cm

Answer 1

(i) Perimeter $=\pi r=\frac{22}{7}\times \frac{2.8}{2}=4.4cm$

Area $=\frac{\pi r^2}{2}=\frac{1}{2}\times \frac{22}{7}\times \frac{2.8}{2}\times \frac{2.8}{2}=3.08{cm}^2$

(ii) Perimeter $=\pi r=\frac{22}{7}\times \frac{56}{2}=88cm$

Area $=\frac{\pi r^2}{2}=\frac{1}{2}\times \frac{22}{7}\times \frac{56}{2}\times \frac{56}{2}=1232{cm}^2$

(iii) Perimeter $=\pi r=\frac{22}{7}\times \frac{84}{2}=132cm$

Area $=\frac{\pi r^2}{2}=\frac{1}{2}\times \frac{22}{7}\times \frac{84}{2}\times \frac{84}{2}=2772{cm}^2$

(iv) Perimeter $=\pi r=\frac{22}{7}\times \frac{112}{2}=176cm$

Area $=\frac{\pi r^2}{2}=\frac{1}{2}\times \frac{22}{7}\times \frac{112}{2}\times \frac{112}{2}=4928{cm}^2$