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Homework Help: Am I wrong or the teacher?

  1. Feb 10, 2012 #1
    Okay, so our teacher gave us to define s=vt. Now i did it like that:
    s=vt=(v_0+at)t=v_0 t+at2, but then, teacher said that's wrong, it should give you s=v_0 t+ \frac{1}{2} at2 Who is wrong me or teacher, If I am wrong, tell me where is my mistake, if the teacher is wrong let me know, thanks!
    Last edited: Feb 11, 2012
  2. jcsd
  3. Feb 10, 2012 #2
    I am assuming that this is a problem concerning the motion of a particle under uniform acceleration. In that case, the teacher is correct. The equation ## s = vt ## is only correct for constant velocity. If velocity is not constant, then you must replace ## v ## with the average velocity.

    Under uniform acceleration, the average velocity is simply ##\frac{v_0+v_f}{2}##.
  4. Feb 10, 2012 #3


    User Avatar

    Staff: Mentor

    You are wrong.

    Are you familiar with calculus? Derivatives and integrals? That's one way to derive those equations.
  5. Feb 10, 2012 #4
    So that would be ##s=vt=\frac{v_0+v_f}{2}t=v_0 t + \frac{1}{2}##at2 or ##s=vt=\frac{v_0+v_f}{2}t=v_f t - \frac{1}{2}##at2
    Last edited: Feb 11, 2012
  6. Feb 10, 2012 #5
    Yes that is correct.
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