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Homework Help: Calculation of work

  1. Nov 18, 2007 #1
    1. The problem statement, all variables and given/known data

    The (non-conservative) force propelling a 1.10 x 10(3)-kg car up a mountain road does 6.80 x 10(6) J of work on the car. The car starts from rest at sea level and has a speed of 22.0 m/s at an altitude of 1.90 x 10(2) m above sea level. Obtain the work done on the car by the combined forces of friction and air resistance, both of which are non-conservative forces.
    Calculate the work done by non-conservative forces using Wnc = dKE +DPE where
    Wnc= W friction+W air+W engine

    2. Relevant equations
    I used W1= .5MV2 + MGH
    required W =W1-W

    3. The attempt at a solution

    .5*1100kg*(22squared m/s) + 1100kg*9.8*192m = 2335960J

    2335960-6800000 = -1655960J
    What did I do wrong?
  2. jcsd
  3. Nov 18, 2007 #2


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    Homework Helper

    Work done on the car - work done by the car = loss of energy due to friction, air resistance.
  4. Nov 18, 2007 #3
    the 2335960-6800000 gives -4464040 which is the correct answer. Too tired to see how unreasonable the first result was!!!
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