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Homework Help: Average Velocity Vector Diagram

  1. Sep 10, 2010 #1
    1. The problem statement, all variables and given/known data

    Untitled-1.png


    2. Relevant equations




    3. The attempt at a solution
    I thought it was "D". The correct answer is "A". Can you help me figure out why?
     
  2. jcsd
  3. Sep 10, 2010 #2
    What was your thought process that led you to believe it was D?
     
  4. Sep 10, 2010 #3
    This is the diagram I used.

    Untitled-2.png
     
  5. Sep 10, 2010 #4
    Ah, I see. You changed the direction on the wrong vector. When subtracting vectors, you want to change the sign of the 2nd vector (the one being subtracted), not the resultant vector. Right now, assuming the velocity components are [tex]\vec{v_1}, \vec{v_2}[/tex], the final vector you drew was:

    [tex]-(\vec{v_2} + \vec{v_1})[/tex]

    when you want:

    [tex]\vec{v_2}-\vec{v_1}[/tex]

    I hope that helps!

    (edit) messed up the subscripts, it should be correct now.
     
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