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Pendulum forces component form

  1. Feb 18, 2015 #1
    1. The problem statement, all variables and given/known data
    Hi, I need help in solving question c) (a pendulum) The required data, problem and relevant equation is in the picture


    3. The attempt at a solution
    I am not sure how to solve it but here are my thoughts:
    since mg is working at j
    y(t)j= mg
    does that mean K(r-L0) x(t) direction?
    I am not sure how to start/think to solve this problem so any tips will be helpfull, thanks!
     

    Attached Files:

  2. jcsd
  3. Feb 18, 2015 #2
    Look at the vector attached to the second term. It is not in the i / x direction but rather in the r direction. It acts directed from the radius of the pendulum. What law describes this force?

    Also, think why do we divide the r vector by its magnitude?
     
  4. Feb 18, 2015 #3
    Is it Hookes law?
    I assume we divide r vector by its magnitude to determine the direction of the force
     
  5. Feb 18, 2015 #4

    lightgrav

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    the rope stretches along its length like a spring. all c) asks you to do is split the diagonal Force into (x,y) components.
     
  6. Feb 18, 2015 #5
    Is mg=y component correct or is it wrong?
    And what force is working in the x direction? Or did I misunderstand what the task is asking for?
     
  7. Feb 18, 2015 #6

    lightgrav

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    mg is entirely vertical ... but most folks treat "up" as positive.
    That is not the ONLY vertical Force contribution, however. The diagonal (spring) Force has x-component and y-component.
     
  8. Feb 19, 2015 #7
    So K(r-L0) works both in x and y direction? Am I then supposed to split the force and find which force works in x and y direction?
     
  9. Feb 19, 2015 #8

    lightgrav

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    the wording in part c) could not be more explicit.
     
  10. Feb 19, 2015 #9
    r(t)=(K*r)i-K*L0j would this be correct?
     
  11. Feb 22, 2015 #10
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