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Homework Help: Forces, displacement, and coordinates of a particle

  1. Sep 29, 2013 #1
    1. The problem statement, all variables and given/known data

    Two forces, vector F 1 = (4 i hat bold + 6 j hat bold) N and vector F 2 = (4 i hat bold + 8 j hat bold) N, act on a particle of mass 1.90 kg that is initially at rest at coordinates (+1.95 m, -3.95 m).

    A) What are the components of the particle's velocity at t = 10.3 s?
    Answer: 43.3i+75.9j
    B) What are the components of the particle's velocity at t = 10.3 s?
    Answer: 60.29°
    C) What displacement does the particle undergo during the first 10.3 s?(Δr)

    D) What are the coordinates of the particle at t = 10.3 s?

    2. Relevant equations

    3. The attempt at a solution
    For C) I have tried every method I could think of to solve for Δr from multiplying the components of the particles velocity (A) by the time, to squaring each part and placing them under a √
    D) I tried a lot for D too. I tried multiplying the coordinates given in the problem above by time, multiplying by the velocity components, and some other methods I cant remember, but nothing has come out right.
  2. jcsd
  3. Sep 29, 2013 #2
    The section titled "relevant equations" is there for a reason. What equations are relevant in this case?
  4. Sep 29, 2013 #3
    If i knew I would use them

    For A) I used F=ma
    For B) I used arctan (Vxf/Vyf)

    For C) the equation I thought might be right was rf=ri + Vit + 1/2at^2, but that was wrong

    And for D) I tried to multiply the time by the velocity components because the seconds would cancel out and I'd be left with meters
  5. Sep 29, 2013 #4
    The equation you mentioned for C) is indeed the equation you should have used. What was the problem with it?
  6. Sep 29, 2013 #5
    Im not sure, I can try it again
    I think I may have been confused on what numbers get plugged in where

    So t=10.3s
    a=4.21i+7.36j m/s^2
    And then im solving for rf-ri

    Is that all correct?
  7. Sep 29, 2013 #6
    You will obtain the displacement vector. It is not entirely clear to me whether C) wants that, or its magnitude, though.
  8. Sep 29, 2013 #7
    Its asking for Δr in meters
  9. Sep 29, 2013 #8
    Then it is probably the magnitude.
  10. Sep 29, 2013 #9
    Thats where you square the values and put them under the radical sign right?
  11. Sep 29, 2013 #10
  12. Sep 29, 2013 #11
    Ok sorry for all the questions but i just wanna make sure im gonna do this right

    So I solve for Δr and put those under the radical sign?
    But since those are vector components I cant add them together
    Am i putting the wrong values under the rad sign?
  13. Sep 29, 2013 #12
    If you are given a vector ## a \vec \imath + b \vec \jmath##, what is its magnitude?
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