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Homework Help: Change in Grav PE with the change in origin.

  1. Feb 28, 2012 #1
    If a 1kg object is 1.5 m heigh. I find its PE to be 14.7 J. If it falls to the ground, the PE of 14.7 J goes to 0 as the object approaches the ground. Right?

    Now say the origin has been moved to 1.5 m where the object lies. Is the object at 0 J at the origin and approaching -14.7 J as it approaches the ground?

    Thanks
     
  2. jcsd
  3. Feb 28, 2012 #2

    gneill

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    Staff: Mentor

    Hi mrhingle, welcome to PF.

    Yes, changes in PE are relative to a chosen zero reference. If you place the zero reference for PE at an origin at a given height, then excursions below that height are associated with negative values for the PE.
     
  4. Feb 28, 2012 #3
    Would both cases be a negative change in PE?
     
  5. Feb 28, 2012 #4

    gneill

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    Staff: Mentor

    ΔPE = PEfinal - PEinitial

    If ΔPE is positive then the change is positive. If ΔPE is negative then the change is negative.
     
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