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Determine the components of P in the i, j, and k directions.

  1. Aug 28, 2013 #1
    1. The problem statement, all variables and given/known data
    As shown, a pole is subjected to three forces: F, P, and T. The force F expressed in Cartesian vector form is F=[5 i+7 j+6 k] N. Force P has magnitude 7.48 N and acts in the direction given by these direction angles: α=143∘, β=57.7∘, and γ=74.5∘ to the x, y, and z axes, respectively. Force T lies within the yz plane, its direction is given by the 3-4-5 triangle shown, and its magnitude is 14 N.
    Determine the components of P in the i, j, and k directions.

    2. Relevant equations
    A_x=Acos(α)
    cos^2(α)+cos^2(β)+cos^2(λ)=1


    3. The attempt at a solution
    Honestly, I'm very confused as to how to approach this problem. I was under the impression that the x component was 0, y component was 8.40 and the z component was 11.2. I solved these by making a 2D plane from the P vector into a 3-4-5 right triangle. 3 on y, 4 on z, and 5 as the hyp.
    I would really appreciate a better explanation of how to approach this question..I think I'm making it more difficult than it is.
    Thank you!
     

    Attached Files:

  2. jcsd
  3. Aug 28, 2013 #2

    rude man

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    Why arer F and T given if P is the only force to be found? It's not as if P is somehow related to T and/or F.
     
  4. Aug 28, 2013 #3
    There are multiple parts to the question.. I'm only asking about the P vector.
     
  5. Aug 28, 2013 #4

    rude man

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    Taking just the x component of P, the only way that component could be zero is if alpha = 90 (or 270) deg.

    Look at P: what is the projection of P along the x axis?
    Hint: cos(α) = P*i/|P|

    (vectors in bold, * signifies dot product)
     
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