(adsbygoogle = window.adsbygoogle || []).push({}); 1. The problem statement, all variables and given/known data

A Yo-Yo is made up of twp solid disks each with radius R and mass M. The axle has radius r and is essentially massless. The Yo Yo is released to unwind.

Find the angular acceleration of the YoYO as it falls in terms of r, R and g.

2. Relevant equations

[tex]\Sigma\tau=I\alpha[/tex]

I = 1/2MR^2

I set up the sum of torques to be the tension from the string times r, plus 2MgR, though I don't see what difference there would be if it were 2Mgr:

[tex]\Sigma\tau=Tr +2MgR=I\alpha[/tex]

I setup the following too:

[tex]\Sigma\F_y = T -2Mg = 2Ma[/tex] To solve for T and substitute into my equation for the sum of torques.

Then solving for [tex]\alpha[/tex] I finally get:

[tex]\frac{g(r+R) + ar}{R^2}[/tex] I don't think my answer should have a term for linear acceleration, unless it's gravity too?

I feel like I'm doing things blindly. I know that the sum of torques should equal the moment of inertia times the angular acceleration, but this business with the different radii is confusing me and I am uncertain as to whether or not what I'm doing makes sense.

UNRELATED: I tried previewing the post after doing some modifications and it shows all out of formatting. Please excuse any oddities.

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# Homework Help: Find angular acceleration of a yoyo

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