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Homework Help: Parallel and perpendicular part of a vector

  1. Sep 3, 2013 #1
    1. The problem statement, all variables and given/known data
    Resolve the force F into

    a) a part perpendicular to AB and

    b) a part parallel to BC

    2. Relevant equations
    a dot b = ab*cos(θ)

    3. The attempt at a solution
    I attached my attempt in the .pdf file. For some reason it is wrong. I don't understand how my reasoning is incorrect.

    The orange square in the picture is a supposed to be a wooden box in the problem, so that detail is not important to the problem.

    Attached Files:

  2. jcsd
  3. Sep 3, 2013 #2


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    Staff Emeritus
    Science Advisor
    Homework Helper

    First, you might want to check the angle given by arctan (3/5).
  4. Sep 3, 2013 #3
    Thanks for pointing that out, but the answer still comes out to be wrong even if I change that. Am I setting up the problem wrong?

    Do you do F*cos(θ) to find a parallel component of F and F*sin(θ) to find a perpendicular part of F in general?
  5. Sep 3, 2013 #4

    Doc Al

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    Staff: Mentor

    Are you sure that your initial diagram is correct? The given answers do not seem to match the diagram.

  6. Sep 3, 2013 #5
    Yes my diagram is correct. It's possible the solutions could be wrong, it's out of an old book... Anyways, I was wondering if my methodology was correct.
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