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Kinetic energy of a kart

  1. Feb 12, 2009 #1
    1. The problem statement, all variables and given/known data
    A fancart of mass 0.8 kg initially has a velocity of < 0.7, 0, 0 > m/s. Then the fan is turned on, and the air exerts a constant force of < -0.4, 0, 0 > N on the cart for 1.5 seconds.

    What is the change in momentum of the fancart over this 1.5 second interval?

    What is the change in kinetic energy of the fancart over this 1.5 second interval?


    2. Relevant equations
    K = 1/2mv2
    K = p2/2m

    3. The attempt at a solution
    I got the change in momentum. It's <-.6,0,0>
    I can't find the change in kinetic energy.
    I tried K = 1/2mv2 and got 0.196
    I also tried p2/2m and got 0.225
     
  2. jcsd
  3. Feb 12, 2009 #2

    Delphi51

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    Homework Helper

    You must find the KE before and after. Take the difference to get the change.
     
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