JAMB - Mathematics (1988 - No. 39)
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
120\(\pi\)cm3
110\(\pi\)cm3
60\(\pi\)cm3
50\(\pi\)cm3
Explication
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
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