(adsbygoogle = window.adsbygoogle || []).push({}); Lagrange Problem redux -- super urgent...

See the attachment to help you visualize this.

A rod of length L and mass m is povoted at the origin and swings in the vertical plane. The other end of the rod is attached/pivoted to the center of a thin disk of mass m and radius r.

OK, I know that the rod can swing and that the disc can swing and rotate.

So for my kinetic energy, I should have a moment of inertia for the rod. According to the text, the disk should have two moments of inertia. Why and what are they?

I suppose my expression for Kinetic Energy should be (Moment of inertia for rod)*(d theta/ dt)^2 + (Moment of inertia for disk)*(d phi/dt)^2 +??

For potential energy, I should have PE = mgh. But h = L/2 (1-cos theta). So PE = 1/2 mgL (1-cos theta). Or should my mass be 2m, since I have both the mass of the rod and the mass of the disk?

If someone could just help with the setup, I can do the Euler-Lagrange equations from there.

Disregard my earlier post... I was totally off-base with my discussion...

Please help soon! I am really struggling with this problem...

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# Homework Help: Lagrange Problem redux - super

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