Question

Length of tape required to cover the edges of a semi-circular disc of radius $10cm$ is

(a) $62.8cm$
(b) $51.4cm$
(c) $31.4cm$
(d) $15.7cm$

Answer 1

The correct option is (b): $51.4cm$

In order to find the length of tape required to cover the edges of a semi-circular disc, we have to find the perimeter of semi-circle.


From the above figure it is clear that,
Perimeter of semi-circle $=$ Circumference of semi-circle $+$ Diameter
$\because$ Circumference of semi-circle $=\frac{2\pi r}{2}$

$=\pi \times r=\frac{22}{7}\times 10=\frac{220}{7}=31.4cm$ [$\because$ radius $=10cm$]

$\therefore$ Total tape required $=$ Perimeter of semi-circle

$=31.4+(2\times 10)=51.4cm$ $[\because$ diameter $=2\times$radius]