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How is energy conserved by magnet lifting a metallic object

  1. May 1, 2015 #1
    Assume a strong permanent magnet is suspended by a string over a metallic object. The magnet is slowly lowered until the object is attracted to the magnet. For this to occur the object acquired both kinetic and potential energy. Since the object comes to rest upon hitting the magnet, I assume the kinetic energy is dissipated as heat within the magnet. But considering only the closed system of the magnet and the object, the end result is a magnet that has acquired heat energy and an object that has acquired potential energy. Please explain how energy is conserved in this closed system.

    Thanks for helping resolve this for a group of us with too much time on our hands.
     
  2. jcsd
  3. May 1, 2015 #2

    Dale

    Staff: Mentor

    The energy stored in the magnetic field is reduced. The reduction in the field's energy is equal to the work done on the object, both the work done increasing its KE and also the work done increasing its gravitational PE.
     
  4. May 1, 2015 #3
    Thank you for answering our question. Bunch of old guys to far removed from Physics 101. We apologize if this was too similar to other posts.
     
  5. May 1, 2015 #4

    Dale

    Staff: Mentor

    No problem! Let us know if you have any follow up questions.
     
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