Question:
A rectangular strip 25 cm × 7 cm is rotated about the longer side. Find the volume of the solid, thus generated.
Solution:
Given :
Rectangular strip has radius, $r=7 \mathrm{~cm}$
Height, $h=25 \mathrm{~cm}$
Volume of the solid, $\mathrm{V}=\pi r^{2} h$
$=\frac{22}{7} \times 7^{2} \times 25$
$=3850 \mathrm{~cm}^{3}$