Question

A cylinder has inner and outer radii of `5 cm` and `11 cm`, respectively, and a mass of `5 kg`. If the cylinder's frequency of counterclockwise rotation about its center changes from `15 Hz` to `6 Hz`, by how much does its angular momentum change?

Answer 1

The change in angular momentum is `=2.064kgm^2s^-1`

Explanation:

The angular momentum is `L=Iomega`

where `I` is the moment of inertia

and `omega` is the angular velocity

The mass of the cylinder is `m=5kg`

The radii of the cylinder are `r_1=0.05m` and `r_2=0.11m`

For the cylinder, the moment of inertia is `I=m((r_1^2+r_2^2))/2`

So, `I=5*((0.05^2+0.11^2))/2=0.0365kgm^2`

The change in angular velocity is

`Delta omega=Deltaf*2pi=(15-6) xx2pi=18pirads^-1`

The change in angular momentum is

`DeltaL=IDelta omega=0.0365 xx18pi=2.064kgm^2s^-1`