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# A metal pipe is 77 cm long. The inner diameter of a cross section is 4 cm, the outer diameter being 4.4 cm (see Fig. 13.11). Find its (i) inner curved surface area,

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 outer diameter being $\small 4.4\hspace{1mm}cm$ (see Fig.  $\small 13.11$). Find its

(i) inner curved surface area,

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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  = $r_2 = 4\ cm$

Inner curved surface area = $2\pi r_2h$

$\\ = 2\times\frac{22}{7}\times2\times77 \\ = 968\ cm^2$

Therefore, the inner curved surface area of the cylindrical pipe is $968\ cm^2$

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