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Force problems

  1. Apr 21, 2013 #1
    Hello, My name is Neil I'm a high school senior in AP Physics C, I'm still taking Pre-Calculus (I know my counselors aren't the brightest) and I'm having trouble with this problem.


    1. The problem statement, all variables and given/known data
    Find the acceleration of the block down the plane.

    I have a picture with a block on an inclined plane with a force vector of frictional force pointing up and parallel to the plane of 10 N

    Also, the degree of incline on the plane is 40 degrees from the horizontal

    The mass is not provided.

    2. Relevant equations

    F=ma
    Fy=0
    Fgy+Fn=0
    Fgy=Fn

    Fgx+Ff=ma

    Fgx=FgCosθ
    Fgy=FgSinθ

    µ=Tanθ
    3. The attempt at a solution

    I have tried setting Ff equal to Fnµ and using it to plug in FgSinθ so that in the equation

    (mgSinθTanθ+mgCosθ)/m=a

    the m get's crossed out since it is in all of the terms, with this I got

    12.79 m/s2

    But since I'm never too sure of myself I researched the problem on line and found this
    http://www.education.com/study-help/article/inclined-planes1/

    which has all of the solutions for what I'm trying to solve. Which let me know that my answer is erroneous. I'd like to know how to solve it, or what did I miss about the problem?
     
  2. jcsd
  3. Apr 21, 2013 #2

    rude man

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    I'll go out on a limb & say it's not solvable unless the coefficient of dynamic friction is given.
     
  4. Apr 21, 2013 #3
    Nah, it's not given.
     
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