Question

Find the volume of the solid produced by rotating this two-dimensional shape using the axis shown.

Please help

Answer 1

Check the picture below.

so the solid produced will be a cylinder with a hole in the middle, like you see in the picture, hmmm so we could get its volume by simply getting the outer cylinder and subtracting the inner cylinder, or we can just get the volume of the ring on the left and multiply it by its length, so let's do the that.

`\textit{volume of a ring}\\\\ V=\pi (R^2-r^2)~~ \begin{cases} R=\stackrel{larger}{radius}\\ r=\stackrel{smaller}{radius}\\[-0.5em] \hrulefill\\ R=3\\ r=1 \end{cases}\implies V=\pi (3^2-1^2)\implies V=8\pi \\\\\\ \stackrel{\textit{\large volume of the hollow cylinder}}{\stackrel{\textit{volume of the ring}}{(8\pi )}\qquad \stackrel{length}{(6)}\implies 48\pi ~~\approx~~150.80}`