Question

A rectangular sheet of dimensions $25cm\times 7cm$ is rotated about its longer side. Find the whole surface area of the solid thus generated.

Answer 1

When a rectangular sheet is rotated about its length, we get a cylinder
where the height of cylinder $=7cm$

and the circumference of the base of the cylinder $=25cm$

Thus curved surface area $=2\pi rh$

$=\left(2\pi r\right)\times h$

$=25\times 7$

$=175c{m}^2$