Conservation of angular momentum on low-friction bearings

[Seraph404]

Homework Statement

Two disks are mounted on low-friction bearings on the same axle and can be brought together so that they couple and rotate as one unit. a) The first disk, with rotational inertia 3.3 kg m^2 about its central axis, is set spinning at 450 rev/min. The second disk, with rotational inertia 6.6 kg m^2 about its central axis, is set spinning at 900 rev/min in the same direction as the first. They then couple together. What is their angular speed after coupling?

Homework Equations

L = L'
L = Iw

The Attempt at a Solution

Can I get some hints on how to find the final rotational inertia? I'm sure it's something simple; I've just sort of been struggling with this chapter. I can't seem to visulize angular momentum at all.

 

[Doc Al]

Can I get some hints on how to find the final rotational inertia?

The rotational inertia of the coupled disks is just the sum of the individual rotational inertias of each disk.

 

[Seraph404]

Then what is the initial rotational inertia?

 

[Doc Al]

Then what is the initial rotational inertia?

The rotational inertia of each disk is given.

Hint: The total angular momentum is the sum of the angular momenta of each disk. (I suspect that's the question you meant to ask.)

 

[Seraph404]

Oh I see. I feel dumb, now.