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Homework Help: Average velocity question?

  1. Jul 24, 2014 #1
    Hey guys I just had a question regarding the equation to calculate average velocity. The first equation i've seen is: Vf+Vi/2, with Vf representing final velocity and Vi representing initial velocity. The second equation i've seen is Xf-Xi/Δt, with X representing position and Δt representing the elapsed time. What is the difference between the two? I get confused on which equation to use for a problem asking for average velocity.
  2. jcsd
  3. Jul 24, 2014 #2

    Doc Al

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    Staff: Mentor

    The first equation, (Vf + Vi)/2, gives the average velocity when the acceleration is constant. It's not true in general.

    The second, (Xf - Xi)/Δt, is the definition of average velocity and is always true. Whether it's useful or not depends on what you are given in the problem.
  4. Jul 24, 2014 #3


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    Notice the parentheses Doc Al added in his reply to you.
  5. Jul 26, 2014 #4
    ok that cleared it up, thanks!
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