Question

A frustum of a cone is $9cm$ thick and the diameters of its circular ends are $28cm$ and $4cm$. Find the volume and lateral surface area of the frustum. (Take $\pi =22/7$)

Answer 1

Volume of frusturn$=\frac{1}{3}\pi h(R^2+r^2+Rr)$

$=\frac{1}{3}\times \pi \times 9({14}^2+2^2+14\times 2)$

$=684\pi c{m}^2$

LSA of frusturn$=\pi (R+r)l=\pi (R+r)\sqrt{{(R-r)}^2+h^2}$

$=\pi (14+2)\sqrt{{(14-2)}^2+9^2}=16\pi \times \sqrt{144+81}=16\pi \sqrt{225}$

$=16\pi \times 15=240\pi c{m}^2$