Question

A solid disk, spinning counter-clockwise, has a mass of `9 kg` and a radius of `3/8 m`. If a point on the edge of the disk is moving at `7/5 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 `=2.36kgm^2s^-1`
The angular velocity is `=3.73rads^-1`

Explanation:

The angular velocity is

`omega=(Deltatheta)/(Deltat)`

`v=r*((Deltatheta)/(Deltat))=r omega`

`omega=v/r`

where,

`v=7/5ms^(-1)`

`r=3/8m`

So,

`omega=(7/5)/(3/8)=3.73rads^-1`

The angular momentum is `L=Iomega`

where `I` is the moment of inertia

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

So, `I=9*(3/8)^2/2=0.63kgm^2`

THe angular momentum is

`L=0.63*3.73=2.36kgm^2s^-1`