Question

A metal pipe is 77 cm long. The inner diameter of a cross section is 4 cm, the outer diameter being 4.4 cm. Find its

(i) inner curved surface area

(ii) outer curved surface area

(iii) total surface area

Answer 1

Let R and r be the outer and inner radii of the metal pipe. Then,

$R=2.2$ $cm$, $r=2$ $cm$, $h=77$ $cm$

$\left(i\right)S_1=2\pi rh=2\times \frac{22}{7}\times 2\times 77=968$ $c{m}^2$

$\left(ii\right)S_2=2\pi Rh=2\times \frac{22}{7}\times 2.2\times 77=1064.8$ $c{m}^2$

$\left(iii\right)TSA=S_1+S_2+2(\pi R^2-\pi r^2)$

$=968+1064.8+2\times \frac{22}{7}\left[\right(2.2{)}^2-2^2]=2028.08$ $c{m}^2$