(adsbygoogle = window.adsbygoogle || []).push({}); 1. The problem statement, all variables and given/known data

A uniformly charged ring has a radius a, lies in a horizontal plane, and has a negative charge given by -Q. A small particle of mass m has a positive charge given by q. The small particle is located on the axis of the ring.

What is the minimum value of q/m such that the particle will be in equilibrium under the action of gravity and the electrostatic force? (Use the following variables as necessary: a, k, Q, and g.)?

2. Relevant equations

I let x = the distance the charge is from the center of the ring.

[tex]E[/tex]=[tex]\frac{kQx}{\sqrt{a^2+x^2}^{3}}[/tex]

3. The attempt at a solution

I started by saying that "mg" must be equal to:

[tex]\frac{kQxq}{\sqrt{a^2+x^2}^{3}}[/tex]

However, I cannot eliminate the x variable from the problem. Am I missing something or do I have the wrong approach altogether?

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# Homework Help: Force due to a uniformly charged ring

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