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Potential energy as a form of mass?

  1. Dec 14, 2016 #1
    1. The problem statement, all variables and given/known data
    Let's say we have a mass of 5kg at a height of 3 m so it's potential energy is mgh = 147J/1.6e-19 = 9.19 e20 eV. Now we know that E = mc^2... so when finding the mass of this potential energy we get 10.2e3 kg. What the hell is that supposed to mean?

    2. Relevant equations
    None
    3. The attempt at a solution
     
  2. jcsd
  3. Dec 14, 2016 #2

    mfb

    User Avatar
    2016 Award

    Staff: Mentor

    Something went wrong with the units here.
    And again here.

    If you fix the calculation, you'll get a result of something like 3.000000000000001 kg (didn't count the zeros). It means total contribution to energy of the overall system (Earth+mass) is not the same as the rest energy of the small test mass.
     
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