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Pole Vaulting Force Question

  1. Feb 7, 2016 #1
    1. The problem statement, all variables and given/known data
    IMG_0053.jpg

    2. Relevant equations
    ΣF=ma

    3. The attempt at a solution
    IMG_0054.jpg

    I drew a free body diagram for a), but am unsure where to go from here. Do I have enough information to rearrange the equations above and solve for FN?
     
  2. jcsd
  3. Feb 7, 2016 #2

    haruspex

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    What are all these different forces? You are making it much more complicated than it is.
     
  4. Feb 7, 2016 #3
    In the Y direction, Fy1 & Fy2 are the forces on the pole from the athlete's hands, mg is the weight of the pole itself and FN is the force the ground exerts on the pole.
     
  5. Feb 7, 2016 #4

    haruspex

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    You do not have any information that allows you to treat the pole and vaulter separately, nor are you asked anything that requires you to do so.
     
  6. Feb 7, 2016 #5
    Okay, so is it as simple as saying that the force from the ground acting on the pole is equal and opposite to the net vertical force? So -1500N?
    Or should it be -1500N + mg of the pole/athlete since the mass of both together was given?

    EDIT: I think my first idea is most likely correct if this is the right way to think about the problem since 1500N is the net vertical force
     
  7. Feb 7, 2016 #6

    haruspex

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    The wording is a little strange, but it says the 1500N is the vertical component of the force from the ground acting on the pole. I do not know why it emphasises or even mentions "net".
    The question asks you to find the total force acting on the pole from the ground. That will not be equal and opposite to one of its own components.
     
  8. Feb 7, 2016 #7
    1500N-mg?
     
  9. Feb 7, 2016 #8

    haruspex

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    To what question is 1500N-mg an answer?

    You are told the vertical force from the ground on the pole. It calls this the net vertical force from the ground on the pole, but net force implies it is the sum of several forces. In what way does the vertical force from the ground on the pole consist of several forces? So I am inclined to ignore the word net there.
    Likewise in the horizontal direction.

    If the vertical force from A on B is Fv and the horizontal force from A on B is Fh, what is the resultant force of A on B?
     
  10. Feb 7, 2016 #9
    a)

    FV + Fh?

    So the force from the ground acting on the pole should be 1500N+700N = 2200N?

    I am obviously very confused... I thought the ground could only apply force to the pole vertically...
     
  11. Feb 7, 2016 #10

    haruspex

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    Yes, as vectors.
    How do you add vectors in different directions?
    If the ground could not apply a horizontal force to the pole then the end of the pole would slide under the bar. Not very convenient for the vaulter.
     
  12. Feb 7, 2016 #11
    Since one is horizontal and one is vertical am I supposed to use pythagorean theorem?
     
  13. Feb 7, 2016 #12

    haruspex

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    Yes.
     
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