Question:
A right triangle with sides 3 cm, 4 cm and 5 cm is rotated about the side of 3 cm to form a cone. The volume of the cone so formed is
(a) 12π cm3
(b) 15π cm3
(c) 16π cm3
(d) 20π cm3
Solution:
Radius of cone VAOB
r = 4 cm
Height of cone VAOB
h = 3 cm
The volume of cone VAOB
$=\frac{1}{3} \pi r^{2} h$
$=\frac{1}{3} \pi(3)^{2} \times 4$
$=12 \pi \mathrm{cm}^{3}$
Hence, the correct answer is choice (a).
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