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Homework Help: Potential/Kinetic Energy

  1. Oct 8, 2008 #1
    1. The problem statement, all variables and given/known data
    A ball drops some distance and loses 30 J of gravitational potential energy. Do not ignore air resistance. How much kinetic energy did the ball gain?

    A. More than 30J
    B. Exactly 30J
    C. Less than 30J
    D. Cannot be determined from the information given.

    2. Relevant equations

    GPE = MGH
    KE = .5mv^2

    3. The attempt at a solution

    I think the answer should be less than 30J, because those are conservative forces, but friction due to air resistance takes some potential energy away. My lab partner says it should be more than 30J, for the same reason. Help?
  2. jcsd
  3. Oct 8, 2008 #2
    i agree that it should be C because the air resistance would restrict it from gaining the full kinetic energy from it's potential energy.
  4. Oct 8, 2008 #3
    C. Less than 30.

    If all the potential energy was transferred to kinetic it would be exactly 30 J,, but since there is air resistance, energy is changed into other forms other than kinetic, leaving less than 30.
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