Question

A cylinder has inner and outer radii of `9 cm` and `16 cm`, respectively, and a mass of `4 kg`. If the cylinder's frequency of counterclockwise rotation about its center changes from `9 Hz` to `4 Hz`, by how much does its angular momentum change?

Answer 1

The change in angular momentum is `=2.12kgm^2s^-1`

Explanation:

The angular momentum is `L=Iomega`

where `I` is the moment of inertia

For a cylinder, `I=m(r_1^2+r_2^2)/2`

So, `I=4*(0.09^2+0.16^2)/2=0.0674kgm^2`

The change in angular momentum is

`DeltaL=IDelta omega`

The change in angular velocity is

`Delta omega=(9-4)*2pi=10pirads^-1`

The change in angular momentum is

`DeltaL=0.0674*10pi=2.12kgm^2s^-1`