Electric Force: Charged Particles Homework Solution

[TheExibo]

Homework Statement

Particles of charge q and 3q are placed 90m away from each other. A third particle is place in between them and the total electric force on this particle is zero. Determine the position of this particle.

Homework Equations

F(E)=(k)(q1)(q2)/(r^2)

The Attempt at a Solution

http://imgur.com/41Ngn8o
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After using the quadratic formula, I get stuck with two answers and I'm sure neigh ter of them are correct. Maybe the negative sign in the forces equation is unnecessary? Thanks

 

[Doc Al]

After using the quadratic formula, I get stuck with two answers and I'm sure neigh ter of them are correct.

What answers did you get? Are both consistent with the constraints of the problem? Why do you think neither are correct?

Maybe the negative sign in the forces equation is unnecessary?

No, the negative sign was not correct, but you somehow managed to cancel it out. Looks to me like your final equation was correct. (Except that you left out a y in one of the terms; I assume that was just a typo.)

You know that the direction of the forces are opposite, so you just need to set the magnitudes equal.

 

[TheExibo]

What answers did you get? Are both consistent with the constraints of the problem? Why do you think neither are correct?No, the negative sign was not correct, but you somehow managed to cancel it out. Looks to me like your final equation was correct. (Except that you left out a y in one of the terms; I assume that was just a typo.)

You know that the direction of the forces are opposite, so you just need to set the magnitudes equal.

It seems the answers in the back weren't exactly correct. Thanks for checking my work!