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Homework Help: Conservative force vs nonConservative force

  1. Nov 5, 2007 #1
    In a given displacement of a particle, its kinetic energy increases by 25 J while its potential energy decreases by 10 J. Determine the work of the nonconservative forces acting on the particle during this displacement.
    a. –15 J b. +35 J c. +15 J d. –35 J e. +55 J

    workdone by non-conservative force
    =change in mechanical energy

    Hence I expect the answer to be c, but it turns up to be a, what is the reason?
    Last edited: Nov 5, 2007
  2. jcsd
  3. Nov 5, 2007 #2


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    Homework Helper

    I agree with you. It should be c) +15J.
  4. Nov 13, 2008 #3
    The answer is -15 joules because the non-conservative force (I'm assuming friction) was acting opposite the direction of movement.

    Friction is fighting whatever force is moving that object, and friction is losing. The loser in a force fight does negative work.

    Think of it like this: Darth Vader always does positive work, because he always wins every fight. Whoever fights Vader does negative work, because Vader PWNS THEM every time.
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