Question

The radii of the ends of a frustum of a right circular cone are 5 metres and 8 metres and its lateral height is 5 metres. Find the lateral surface and volume of the frustum.

Answer 1

Lateral surface area of frustum

\[= \pi\left( r + R \right)l\]

\[ = \pi\left( 5 + 8 \right) \times 5\]

\[ = 204 . 28 m^2\]

Height of cone

`h = sqrt(5^2 - (R -r)^2)`

`=sqrt(5^2 - (8-5)^2)`

`=sqrt13`

Volume `=(pi xx sqrt13)/3 (8^2 + 5^2 + 40) = 540.56 cm^3`.