Question

The radii of the ends of a frustum of a cone are $28cm$ and $7cm$. The height of the cone is $40cm$, find its volume.

• A. $32340c{m}^3$
• B. $43120c{m}^3$
• C. $10780c{m}^3$
• D. $2156c{m}^3$

Answer 1

The correct option is B $43120c{m}^3$

If $R$ and $r$ are the top and bottom radii of frustrum then,

$\text{Volume of frustum}=\frac{1}{3}\pi h[R^2+r^2+Rr]=\frac{1}{3}\times \frac{22}{7}\times 40[{28}^2+7^2+28\times 7]$

$=\frac{1}{3}\times \frac{22}{7}\times 40\times 1029=43120{cm}^3$