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Total potential energy due to gravitational and electrostatic potential energy

  1. Feb 10, 2011 #1
    1. The problem statement, all variables and given/known data
    Two dust particles are separated by 0.01m and of the same mass and charge, find the total potential energy


    2. Relevant equations
    [tex]E_{el}=k\frac{q_1 q_2}{r}[/tex]

    [tex]E_{grav}=-G\frac{m_1 m_2}{r}[/tex]

    [tex]r=0.01 m[/tex], [tex]q_1=q_2=1.1201\times10^{-18} C[/tex] [tex]m_1=m_2=13\times10^{-9} kg[/tex]
    Where G and k are the gravitational and Coulomb's constant respectively.

    3. The attempt at a solution

    [tex]E_{el}=1.128\times10^{-24} J[/tex]

    [tex]E_{grav}=-1.128\times10^{-24} J[/tex]

    Not sure whether it [tex]E_{tot}=E_{el}+E_{grav}[/tex] or [tex]E_{tot}=\left|E_{el}\right|+\left|E_{grav}\right|[/tex]?
     
  2. jcsd
  3. Feb 10, 2011 #2

    supratim1

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    Gold Member

    you have found the electric and gravitational field. now calculate the potentials. total will be the sum of the potentials, not sum of their magnitudes.
     
  4. Feb 16, 2011 #3
    So the potential energy of the system is zero?
     
  5. Feb 17, 2011 #4

    supratim1

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    Gold Member

    why should it be zero?
     
  6. Feb 17, 2011 #5
    Well I have found the electrostatic and gravitational potential energies

    [tex]E_{el}=1.128\times10^{-24} J[/tex]
    and
    [tex]E_{grav}=-1.128\times10^{-24} J[/tex]

    Is it not their sum? I'm taking [tex]r=0[/tex] as the particles being together and [tex]E_{pot}=0[/tex] at [tex]r=\infty[/tex]
     
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