If a metal pipe 10cm long has an external diameter of 12cm and a thickness...

JAMB 1988

If a metal pipe 10cm long has an external diameter of 12cm and a thickness of 1cm find the volume of the metal used in making the pipe

A. 120\(\pi\)cm³
B. 110\(\pi\)cm³
C. 60\(\pi\)cm³
D. 50\(\pi\)cm³

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Correct Answer: Option B

Explanation

The volume of the pipe is equal to the area of the cross section and length.

let outer and inner radii be R and r respectively.

Area of the cross section = (R² - r²)

where R = 6 and r = 6 - 1

= 5cm

Area of the cross section = (6² - 5²)\(\pi\) = (36 - 25)\(\pi\)cm sq

vol. of the pipe = \(\pi\) (R² - r²)L where length (L) = 10

volume = 11\(\pi\) x 10

= 110\(\pi\)cm³

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