Question
A right-angled triangle whose sides are 6 cm, 8 cm and 10 cm is revolved about the sides containing the right angle in two ways. Find the difference in volumes of the two solids so formed.

Answer

Three sides of a triangle are $6 cm , 8 cm$ and $10 cm$.
Case (i): If the triangle is revolved about the side $6 cm$, the cone will be formed with radius 6 $cm$ and height $8 cm$.

Volume of the cone $=\frac{1}{3} \pi r ^2 h$ cu. units
$
\begin{aligned}
& =\frac{1}{3} \times \pi \times 6 \times 6 \times 8 \\
& =96 \pi cm ^3
\end{aligned}
$

Case (ii): If the triangle is revolved about the side $8 cm$, the cone will be formed with radius 8 $cm$ and height $6 cm$.

Volume of the cone $=\frac{1}{3} \times \pi \times 8 \times 8 \times 6$
$
=128 \pi cm ^3
$
Difference in volume of the two solids
$
\begin{aligned}
& =(128 \pi-96 \pi) cm ^3 \\
& =32 \pi cm ^3
\end{aligned}
$
$
\begin{aligned}
& =32 \times \frac{22}{7} cm ^3 \\
& =100.57 cm ^3
\end{aligned}
$
The difference in the volume of the two solids $=100.57 cm ^3$

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