# The frequency of two parallel springs and one weight system

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1. May 10, 2017

### ltnghia1304

1. The problem statement, all variables and given/known data
I want to find the angular frequency of the system below

2. Relevant equations
F = -kx
U = 1/2*k*x^2

3. The attempt at a solution

But here's the answer:

I dont know how come this solution. Any one help me? Thank you so much.

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Last edited: May 10, 2017
2. May 11, 2017

### haruspex

I do not understand even your first equation. It looks like a sum of moments about left hand end equals zero. But there will be an angular acceleration here, and the system has a moment of inertia about that axis.
About what point does it not have any MoI?

3. May 11, 2017

### ltnghia1304

Yes I used the sum of moments. Actually I also havent get the point of this problem. Just think that it will be balance like that

4. May 11, 2017

### haruspex

OK, but the standard equation, relative to a specified axis, is Σmoment=MoI * angular acceleration. The bar will in general have an angular acceleration, and the MoI of the bar+mass about the ends of the bar is not zero. So the sum of the moments will not be zero.
As I asked before, about what axis does the bar+mass have zero MoI?