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Physics poof

  1. Feb 24, 2008 #1
    1. The problem statement, all variables and given/known data

    Prove that if the acceleration is constant, the average velocity=vf+vi/2

    2. Relevant equations
    average velocity=xf-xi/change in t
    xf=xi+vit+1/2at^2
    vf^2=vi^2+2a(xf-xi)



    3. The attempt at a solution

    I started out by drawing a diagram:

    _ _ _ _ _ _ _ _ _
    Vi v vf
    20km/h 20km/h

    20+20/2=20

    Do you think this proves it or is there another way of doing it?

    Thank you in advance
     
  2. jcsd
  3. Feb 25, 2008 #2
    Could someone please help me on this?

    Thank you very much
     
  4. Feb 25, 2008 #3
    Can you use calculus or not?
     
  5. Feb 25, 2008 #4
    vf = vi + at
    Now if a=constant, the graph of velocity plotted against time is a straight line, yes? (From the equation above)
    Now it is obvious that the average velocity between vf and vi must be (vf + vi)/2 from the graph.
    Otherwise you can use calculus to find the time average of the velocity function.
     
  6. Feb 26, 2008 #5
    Thank you very much

    Regards
     
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