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Need help determining F and n in terms of variables

  1. Feb 17, 2009 #1
    1. The problem statement, all variables and given/known data
    A box of mass (m) is held against a frictionless wall by a force of magnitude F at an angle [tex]\theta[/tex] (above right). Determine F in terms of whatever variables are necessary. Similarly, determine the magnitude of the normal force (n) in terms of whatever variables are necessary. (Hint: you can only have m, [tex]\theta[/tex], and g in your answers)


    2. Relevant equations



    3. The attempt at a solution
    F=ma, a=g
    F=mg


    n=F?
     
  2. jcsd
  3. Feb 17, 2009 #2

    LowlyPion

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    Homework Helper

    They want you to resolve the Force into the horizontal and vertical components of force necessary to hold the box with no net force.

    If you don't have a sinθ or cosθ in your answer you can be certain it isn't correct.
     
  4. Feb 17, 2009 #3
    so Fx=Sin[tex]\theta[/tex] and Fy=mg

    I know the answer is F=mg/sin [tex]\theta[/tex], but I thought you divide Fx by Fy? So why is the answer F=mg/sin [tex]\theta[/tex]?
     
  5. Feb 17, 2009 #4

    LowlyPion

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    Not quite, because they defined the angle θ with respect to "rightward" axis. Hence the component that balances the m*g is going to be the vertical sinθ component.
     
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