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Homework Help: Need Help With Newton's Second Law (Net Force) Problem

  1. Feb 6, 2012 #1
    1. The problem statement, all variables and given/known data

    Okay, so I was given a diagram that looks like the one I linked to above.
    This is pretty basic, using Newton's second law to find-

    A) the weight of the "lamp"
    B) the tension in the chain

    The strut is exerting a force of 110 N, the angle between the strut and the ceiling is 55 °.

    Thanks so much!

    ***ALSO the diagram says 11 N, the correct force is 110 N
  2. jcsd
  3. Feb 6, 2012 #2
    Resolve all the forces into x and y components

    Then it should be trivial

    Hope this helps
  4. Feb 6, 2012 #3
    This, but start with a free body diagram as well. They are seriously helpful, and should help you resolve the components.
  5. Feb 6, 2012 #4
    I've done a free body diagram. I am still confused as to how to find the weight of the lamp. Does the combined force of the chain and the pull of the lamp have to equal 110 N?
  6. Feb 6, 2012 #5
    Try setting up a system. The force of tension in the diagonal string has to compensate for two perpendicular forces since the system is not accelerating.

    To answer your question, the chain is completely horizontal, which means the tension in the chain cannot influence the pull of the lamp or visa versa. The chain is balanced horizontally by the horizontal component of the diagonal string.
  7. Feb 6, 2012 #6
    Using some basic trig you can find the x and y components of the 110N that you are given. Then think about how this force is going to be balanced by the chain and lamp weight so it is in equilibrium (net force=0)
  8. Feb 6, 2012 #7

    There's my fbd and hopefully correct components, sorry its small.
    So does the weight of the lamp have to be equal to the y component and the chain equal to the x component but in the negative direction?

    If I seem slow it's because this is my first experience with problems like these.. so bear with me.
  9. Feb 6, 2012 #8
    Very good. Yes you are correct. The y component of the Tension force in the diagonal string has to be equal to the force of gravity on the lamp, and the x component of Tension force has to be equal to the tension in the chain. Setup your equations and you're done (and can solve for what you're looking for).
  10. Feb 6, 2012 #9
    awesome, thanks!
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