1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Homework Help: The frequency of two parallel springs and one weight system

  1. May 10, 2017 #1
    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.

    Attached Files:

    Last edited: May 10, 2017
  2. jcsd
  3. May 11, 2017 #2


    User Avatar
    Science Advisor
    Homework Helper
    Gold Member

    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?
  4. May 11, 2017 #3
    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
  5. May 11, 2017 #4


    User Avatar
    Science Advisor
    Homework Helper
    Gold Member

    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?
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted