Q5 of 20 Page 225

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 figure) Find its

(i) inner curved surface area


(ii) outer curved surface area


(iii) Total surface area.


Given, A metal pipe is 77 cm. long

Inner Diameter = 4cm i.e. r = 2cm


Outer diameter = 4.4cm i.e. R = 2.2cm


(i) inner curved surface area = 2πrh


= 2 × 3.14 × 2 × 77


= 967.6cm2


(ii) outer curved surface area = 2πRh


= 2 × 3.14 × 2.2 × 77


= 1063.8cm2


(iii) total surface area = 2πrh + 2πrh + 2π(R2 – r2)


= 967.6 + 1063.8 + 2 × 3.14 × (2.22 – 22)


= 2036.6cm2


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