I'm more having a problem of what they actually want and what I can use/assume. The question is:(adsbygoogle = window.adsbygoogle || []).push({});

A horizontal disk of moment of inertia I rotates frictionlessly around its axis. A massless pulley of radius r which shares the axis of rotation is attached to the disk. A massless string is wound around the pulley, passed over another massless frictionless pulley, and attached to a hanging mass m.

There are two pictures, one of a rotating disk from above with Ft pointing out from it. And the second of a hanging mass from the side with Ft pointing up and mg pointing down from the mass.

a) write down equation of motion for rotating disk. Denote angular acceleration by alpha.

I just have F(tension) = I * alpha. I think thats all it is.

b) Write down the equation of motion for the hanging mass. Its acceleration a is related to ang acc. of disk by a = r*alpha.

Do I just plug in a/r for alpha?

C) Solve equations for a) and b) for Ft and alpha. (Express answers in terms of known quantities, namely, I, r, m, and g.)

This is the one im confused about since for b) i dont have an alpha. Also isnt Ft = mg ? Maybe im making this harder that it actually is. All my other problems were a lot harder for this to be as simple as I have it.

I appreciate the help.

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# Homework Help: Moment of inertia

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