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Need help adding vectors -please help

  1. Feb 8, 2008 #1
    Need help adding vectors --please help

    1. The problem statement, all variables and given/known data
    i have 3 force vectors i want to add to get the resultant.
    vector a mag=1.31N and is 51.34deg to the x-axis (Quad 1)
    vector b mag= 1.31N and is 51.34deg to the x-axis (Quad 4)
    vector c mag = .719N and is along the pos y axis

    how do you add these for resultant???
    ive learned this before but forgot how to add them, --isnt there a simple way to get the one resultant vector?
    thanks for any help!



    2. Relevant equations



    3. The attempt at a solution
     
  2. jcsd
  3. Feb 8, 2008 #2
    also, the forces are from point charges, so no gravity
     
  4. Feb 8, 2008 #3

    Dick

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    Split them all into x and y components and then add the components to get the components of the sum.
     
  5. Feb 8, 2008 #4
    thanks for the reply.

    ok but isnt there a faster way to get the resultant rather than breaking them apart then putting back together again?
     
  6. Feb 8, 2008 #5
    Fxa = 1.31N * cos 51.34deg = .818353N
    Fxb = 1.31N * cos 51.34deg = .818353N
    Fxc............................ = 0 (because force is along the y-axis)

    Fya = 1.31N * sin 51.34deg = 1.0229N
    Fyb = 1.31 * sin51.34deg = 1.0229N
    Fyc = .719N = .719N (because along the y-axis)
     
  7. Feb 8, 2008 #6
    ok so, I broke them down into x and y components. just need help adding them now?
    thanks!
     
  8. Feb 8, 2008 #7
    I'm pretty sure you have to use basic trig functions to find the lengths. Then, add them together.
     
  9. Feb 8, 2008 #8

    Dick

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    Ok, so now add all of the x's and all of the y's. That gives you the x and y components of the total force T. Do you need to get the total magnitude and direction of T? Do you know how to do that?
     
  10. Feb 8, 2008 #9
    yeah total magnitude is what i want.
    So Fx = 1.636706
    Fy = 2.7648

    ho do i add them? thanks
     
  11. Feb 8, 2008 #10

    Dick

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    Good so far. You don't 'add' them. The vector is (Fx,Fy). The magnitude is sqrt(Fx^2+Fy^2), the angle is arctan(Fy/Fx). It's the opposite of splitting into components, you are 'recombining' the components.
     
  12. Feb 9, 2008 #11
    oh duh. this is just pythagarus isnt it? i mean x and y components mean i just get the hypotenuse and thats how you "add" them right>?
    so, sq rt Fx^2 + Fy^2 = resultant vector
     
  13. Feb 9, 2008 #12
    i mean the MAGNITUDE of the vector at least.
     
  14. Feb 9, 2008 #13

    Dick

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    Yes. You are on the right track.
     
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