# Help with rotational dynamics

#### Axel H

1. Homework Statement

http://imageshack.us/photo/my-images/545/rotacion1.jpg/
Translation: Determinate, for the system of Fig. 10-39 the angular velocity of the disk and the linear velocity of m and m'. Calculate the tension in each string. Suposse that m = 600 g, m' = 500 g, M = 800 g, R = 8 cm and r = 6 cm.

2. Homework Equations

3. The Attempt at a Solution
The problem is I don't know to get the moment of inertia because I have the mass of one disk only.

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#### Spinnor

Gold Member
I agree, it looks like you were not given enough information.

One could assume that M was for both discs, but you would still need to know the thicknesses of the two discs which you could estimate if you had to.

Solve the problem assuming that M is the mass of the whole pulley that consist of two disk-form parts of the same thickness, made of the same material. Usually the problem writers think in 2D where thickness does not exist. 