3 Equal Charges in Equilateral Triangle - Find KE @ Inf

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SUMMARY

The discussion focuses on calculating the kinetic energy of three equal charges positioned at the vertices of an equilateral triangle as they move to infinity. The user attempts to derive the potential energy using the integral of the force, represented by the equation F = k * q^2 / r^2, but encounters issues with the integration process. The user correctly identifies the need to account for the geometry of the triangle, specifically using cos 30 degrees and the relationship between dr and ds, but struggles with the application of these concepts in the integral.

PREREQUISITES
  • Understanding of Coulomb's Law (F = k * q^2 / r^2)
  • Familiarity with integral calculus and its application in physics
  • Knowledge of potential energy concepts in electrostatics
  • Basic geometry of equilateral triangles and trigonometric functions
NEXT STEPS
  • Review the derivation of potential energy in electrostatic systems
  • Study the application of integrals in physics, particularly in force and energy calculations
  • Explore the relationship between distance changes (dr and ds) in multi-body systems
  • Learn about the implications of symmetry in electrostatic problems
USEFUL FOR

Students studying electromagnetism, physics educators, and anyone interested in advanced electrostatic calculations involving multiple charges.

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Homework Statement



Question is attached.

I know there's a few ways to solve this, but I'm wondering specifically why my integral of F ds isn't working.

Homework Equations



F = k * q^2 / r^2
U = ∫ F ds
cos 30 = √3/2
s= rcos30

The Attempt at a Solution



U = 2 * cos 30 * k * q^2 ∫ 1/r^2 ds
U = √3 * k * q^2 ∫ 1/r^2 * √3/2 dr - (a to inf)
U = 3/2 * k * q^2 * 1/a
 

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Any help would be appreciated. No one seems to be able to help me.
 
I assume your model is to let all three move apart some small amount, symmetrically. dr will be the increase in distance between any pair, while ds is the distance each moves. If so, I get dr = ds √3, which does not seem to be what you have used.
 

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