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Potential Energy Clarification

  1. Jun 20, 2009 #1
    You lift a ball at constant velocity from a height hi to a greater height hf . Considering the ball and the earth together as the system, which of the following statements is true?

    1. The potential energy of the system increases.
    2. The kinetic energy of the system decreases.
    3. The earth does negative work on the system.
    4. You do negative work on the system.
    5. The source energy of the ball increases.
    6. Two of the above.
    7. None of the above.

    Am I right in thinking that neither 1 nor 2 are correct because the question takes into account BOTH the earth and the ball? They would only be correct if the system was merely the ball, right?
  2. jcsd
  3. Jun 20, 2009 #2
    I believe you are right there.
  4. Jun 20, 2009 #3

    Doc Al

    User Avatar

    Staff: Mentor

    No, gravitational potential energy is a joint property of earth and ball (since gravity is an interaction between them). So #1 is correct.
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