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Total potential energy due to gravitational and electrostatic potential energy

  • Thread starter bobred
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  • #1
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Homework Statement


Two dust particles are separated by 0.01m and of the same mass and charge, find the total potential energy


Homework 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.

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]?
 

Answers and Replies

  • #2
supratim1
Gold Member
279
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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.
 
  • #3
173
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So the potential energy of the system is zero?
 
  • #4
supratim1
Gold Member
279
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why should it be zero?
 
  • #5
173
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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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