Question:
The curved surface area of a right circular cone of height 15 cm and base diameter 16 cm is
(a) 60π cm2
(b) 68π cm2
(c) 120π cm2
(d) 136π cm2
Solution:
Height,
$h=15 \mathrm{~cm}$
$r=\frac{16}{2}$
$=8 \mathrm{~cm}$
$l=\sqrt{r^{2}+h^{2}}$
$=\sqrt{8^{2}+15^{2}}$
$=\sqrt{64+225}$
$=\sqrt{289}$
$l=17 \mathrm{~cm}$
The C.S.A. of cone
$=\pi r l$
$=\pi \times 8 \times 17$
$=136 \pi \mathrm{cm}^{3}$
Hence, the correct answer is choice (d).