The frequency of two parallel springs and one weight system

  • #1

Homework Statement


I want to find the angular frequency of the system below
18426564_1972065893013072_43662875_o.jpg

Homework Equations


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

The Attempt at a Solution


18426570_1972072309679097_1115670989_o.jpg

18472001_1972072313012430_1129210577_o.jpg


But here's the answer:
18426731_1972065903013071_83517209_o.jpg


18426790_1972065909679737_1688739849_o.jpg


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

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Answers and Replies

  • #2
haruspex
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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
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?
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
haruspex
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I used the sum of moments
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?
 

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