Originally Posted by **Pmb** Forum rules require that you must post your attempt to solve the problem before we can help you. Otherwise we'd be doing peoples homework.
Is this a calculus based text that you're using? We can give hints as to how to start. If you know calculus then I'd suggest portioning the cylinder into infinitesimal pieces as a first step. |

No, i don't want the solution, only some hints. :-)

If $\displaystyle L$ is the length and $\displaystyle \rho$ is the density of the cylinder, then $\displaystyle dm= \rho \cdot 2 \pi r dL$. (I used the formula of perimeter because it is a hollow cylinder, am I right?)

But how can it help me?

EDIT: I am wrong, it would be dimensionally wrong, so:

$dm= \rho \pi dr^2 dL$