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Mechanical Energy

  1. Dec 9, 2008 #1
    Given an parachuter and the system parachuter-parachute-Earth and taking in account the resistance of the air, my question is: is the mechanical energy of the system (parachuter.parachute.Earth) a constant, please explain. And please don't talk just about the parachuter because I wan't to know about the parachuter and Earth as one system.
    Thank you in advance.
  2. jcsd
  3. Dec 9, 2008 #2

    Doc Al

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    Staff: Mentor

    What do you think?
  4. Dec 10, 2008 #3
    I think it isn't conserved because of the transformation of that energy in heat
  5. Dec 10, 2008 #4

    Doc Al

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    Staff: Mentor

    Good. You've answered your own question.

    If the parachutist jumped in a vacuum, his kinetic energy would increase as the gravitational PE of the system decreased. Since there'd be no dissipative forces, the total mechanical energy would remain constant.

    But with air drag present, much of his kinetic energy is transformed into random motion of the air--"thermal" energy. (The air gets stirred up, it and the parachute get warmer.) So the net mechanical energy of the system decreases.
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