# A cylinder has inner and outer radii of #8 cm# and #16 cm#, respectively, and a mass of #6 kg#. If the cylinder's frequency of counterclockwise rotation about its center changes from #2 Hz# to #7 Hz#, by how much does its angular momentum change?

##### 1 Answer

The nasty part of this problem is in coming up with the moment of inertia for a thick-walled cylinder rotating along an axis through its centre. This is

where

In this case,

Now, the angular momentum is defined as the product of its moment of inertia multiplied by the angular momentum (in radians/s don't forget!).

Since 1 Hz is equivalent to 2

(Hope you don't mind that I held back on the units until the last line. I thought they would make things a bit messy!)