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Homework Help: Vectors and Acceleration

  1. Sep 16, 2008 #1
    1. The problem statement, all variables and given/known data
    Three forces in the x-y plane act on a 3.40 kg mass: 9.10 N directed at 25o, 12.40 N directed at 156o, and 4.70 N directed at 259o. All angles are measured from the positive x-axis, with positive angles in the Counter-Clockwise direction. Calculate the magnitude of the acceleration.



    2. Relevant equations

    F=ma
    Rx = F1cos(theta) - Quadrant 1
    Ry = F1sin(theta) - Quadrant 1
    R = (Rx^2 + Ry^2)^1/2


    3. The attempt at a solution

    I tried to find the x and y components of each force. Then I added the square of the x-components and took the square root of that answer and I did the same with the y-components. Finally I took the answers from the last step and took the square of them and then the square root of them added. Finally I plugged in that force into F=ma and tried to solve for a, but it doesnt work. I think Im doing something wrong, in that Im not sure what to do about the x,y components that are negative.
     
  2. jcsd
  3. Sep 17, 2008 #2

    tiny-tim

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    Science Advisor
    Homework Helper

    Hi ganondorf29! :smile:
    ah … that's where you're going wrong …

    these are vectors, so you use ordinary vector addition …

    just add the x-components without squaring first. :smile:
     
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