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Homework Help: Three forces simultaneously acting on an object

  1. Oct 26, 2009 #1
    1. The problem statement, all variables and given/known data

    Forces of 10.5 N north, 19.3 N east, and 15.4 N south are simultaneously applied to a 3.81 kg mass as it rests on an air table. What is the magnitude of its acceleration?

    2. Relevant equations


    3. The attempt at a solution
    Well I got the resultant force for the y direction to be 4.9N South. And from here I have no idea what to do, I started drawing triangles of the forces and just placing diagonal lines just so i can connect them, while knowing I cant mathematically do that.

    Thanks for the help!
  2. jcsd
  3. Oct 26, 2009 #2


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    Homework Helper

    Using the relevant equation, find ay along North-south direction.
    Similarly find ax.
    ax and ay are perpendicular to each other. So find the resultant a.
  4. Oct 26, 2009 #3
    would I use the force of gravity as a part of the ay force? So it would be 15.4 + (force gravity) - 10.5?
  5. Oct 26, 2009 #4
    I wouldn't think you would use gravity. This problem is looking acceleration in the plane (N/S & E/W).

    You should just use the forces and mass the give you:

    \left(\frac{ \sum F_{N,S}}{m}\right)^2+\left(\frac{\sum F_{E,W}}{m}\right)^2=a^2

    and make sure you keep you signs correct.
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