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Work, energy, power!

  1. Dec 15, 2007 #1
    1. The problem statement, all variables and given/known data

    A body of mass m is accelerated uniformly from rest to speed v in time T. The instantaneous power delivered to the body as a function of time is given by?

    2. Relevant equations

    P=w/t

    e=1/2mv^2


    3. The attempt at a solution

    P=w/t
    P=[0.5m(v/T)^2 ] /t
    p=(mv^2) / (tT^2)


    Comments:
    The answer given is (mv^2)t / (T^2).
    Can anyone tell me where i went wrong?
     
  2. jcsd
  3. Dec 15, 2007 #2

    Dale

    Staff: Mentor

    P=[0.5m(v/T)^2 ] /t

    v/T is not in units of m/s. You should always check your units.

    However, I would use a different formula, I would use P = F v. Or, more explicitly for this problem P(t) = F v(t)
     
  4. Dec 15, 2007 #3

    Shooting Star

    User Avatar
    Homework Helper

    Just a bit of algebraic jugglery. Let Vf be the final velo, and v the instantaneous velo.

    P(t) = Fv = mav = ma^2t, since v=at. But Vf = aT. So, a = Vf/T, which gives,
    P(t) = m(Vf/T)^2t.
     
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