Question

Find the perimeter and area of semicircles(Half cut rings) whose radii are
i) $35$ cm
ii) $10.5$ cm
iii) $6.3$ m
iv) $4.9$ m

Answer 1

(i) Perimeter $=\frac{2\pi r}{2}=\frac{2}{2}\times \frac{22}{7}\times 35=110cm$

Area $=\frac{1}{2}\times \pi r^2=\frac{1}{2}\times \frac{22}{7}\times 35\times 35=1925{cm}^2$

(ii) Perimeter $=\pi r=\frac{22}{7}\times 10.5=33m$

Area $=\frac{1}{2}\times \pi r^2=\frac{1}{2}\times \frac{22}{7}\times 10.5\times 10.5=173.25{cm}^2$

(iii) Perimeter $=\pi r=\frac{22}{7}\times 6.3=19.8cm$

Area $=\frac{1}{2}\pi r^2=\frac{1}{2}\times \frac{22}{7}\times 6.3\times 6.3=62.37m^2$

(iv) Perimeter $=\pi r=\frac{22}{7}\times 4.9=15.4m$

Area $=\frac{1}{2}\pi r^2=\frac{1}{2}\times \frac{22}{7}\times 4.9\times 4.9=37.73m^2$