Rotational motion: rod in a tube

[SonOfOle]

Homework Statement

A long thin tube of negligible mass is pivoted so it may rotate freely without friction in a horizontal plane. A thin rod of mass M and length L lies in the tube and can slide without friction in the tube. ($$I_{Thin Rod}=\frac{1}{12}ML^{2}$$).

Find the equations of motion for the thin rod in terms of the angle of the tube, $$\theta$$, and the radial position of the center of the rod, r.

 

[calef]

Could you perhaps draw a diagram of what you're asking? I'm a little confused by your description, because you could be describing a number of different systems.

 

[SonOfOle]

The diagram is attached. Thanks for any help. I'm currently stumped.