Question

A solid disk, spinning counter-clockwise, has a mass of `8 kg` and a radius of `5/2 m`. If a point on the edge of the disk is moving at `15/4 m/s` in the direction perpendicular to the disk's radius, what is the disk's angular momentum and velocity?

Answer 1

The angular momentum is `=235.6kgm^2s^-1`
The angular velocity is `=9.42rads^-1`

Explanation:

The angular velocity is

`omega=v/r`

where,

`v=15/4ms^(-1)`

`r=5/2m`

So,

`omega=(15/4)/(5/2)*2pi=3pi=9.42rads^-1`

The angular momentum is `L=Iomega`

where `I` is the moment of inertia

For a solid disc, `I=(mr^2)/2`

So, `I=8*(5/2)^2/2=25kgm^2`

`L=9.42*25=235.6kgm^2s^-1`