Q : 3    A metal pipe is $\small 77\hspace{1mm}cm$ long. The inner diameter of a cross section is $\small 4\hspace{1mm}cm$, the outerdiameter being  $\small 4.4\hspace{1mm}cm$ (see Fig. $\small 13.11$). Find its              (ii) Outer surface area.

N Nehul

Note: There are two surfaces, inner and outer.

Given,

Height of the cylinder, $h = 77\ cm$

Outer diameter  = $r_1 = 4.4\ cm$

Inner diameter  = $r_2 = 4\ cm$

Outer curved surface area = $2\pi r_1h$

$\\ = 2\times\frac{22}{7}\times2.2\times77 \\ = 1064.8\ cm^2$

Therefore, the outer curved surface area of the cylindrical pipe is $1064.8\ cm^2$

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