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Stability of a teeter-toy-classical mechanics

  1. Jan 7, 2016 #1
    1. The problem statement, all variables and given/known data:
    teeter.totter-expl.c.jpg

    In the image above, the toy consists of two identical mass hanging from a peg. we take the zero potential energy at the pivot.



    2. Relevant equations:
    http://www.physicsmynd.com/?p=1172


    3. The attempt at a solution
    Since the potential energy is zero at the pivot, and the potential energy is defined by U(θ)=mgh, I had:
    U(θ)= mg(- l*cos(α+θ)- l*cos(α-θ))
    but the solution is: U(θ)= mg(L*cos(θ) - l*cos(α+θ)) +mg(L*cos(θ) - l*cos(α-θ))

    So my question is,what is wrong with my answer, and why?
     
  2. jcsd
  3. Jan 7, 2016 #2

    TSny

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    The zero of PE is at the pivot point.
    l*cos(α-θ) is not the vertical distance between the pivot point and the mass on the right.
     

    Attached Files:

  4. Jan 9, 2016 #3
    Thank you very much sir, I think my problem was with English more than it was with physics, I thought what he meant be pivot is the joining point of the arms with the peg, now I got the solution right.
     
  5. Jan 9, 2016 #4

    TSny

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    OK. Good.
     
  6. Oct 14, 2016 #5
    Hello, could you please publish or send to me the correct solution to that example?
     
  7. Oct 14, 2016 #6
    Hello, could you please publish or send to me the correct solution to that example?
     
  8. Oct 15, 2016 #7

    haruspex

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    That's not how things are done here. If you have been given the same homework task and need help, please post your own attempt; maybe in a new thread.
     
  9. Oct 18, 2016 #8
    Can someone do all my physics homeworks please and post them to me on time and not a minute late ?
     
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