- #1

oreosama

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## Homework Statement

Three rods each of uniform charge Q and length a are formed into an equilateral triangle. Given[Q,a,q] determine:

1. The voltage at the center of the triangle.

2. If a charge -q is placed at the center of the triangle determine potential energy.

3. Determine the initial speed of the -q in order that it exits the system and never returns.

## Homework Equations

[tex]V = \frac{1}{4 \pi \epsilon_0} \int \frac{dq}{r}[/tex][tex]U = Vq[/tex]

[tex]K_0 + U_0 = K + U[/tex]

## The Attempt at a Solution

http://i.imgur.com/7IZ3PbP.png

I take 1 half of bottom rod and intend to integrate for V[tex]dq = Q \frac{dx}{a}[/tex]

[tex]r = \sqrt{y^2 + (\frac{a}{2} - x)^2}[/tex]

using the V formula above this integrates(from 0 to a/2) to[tex]V = \frac{Q}{4 \pi \epsilon_0}[\ln{\frac{a+\sqrt{\frac{a^2}{4} + y^2}}{y}}][/tex]

since this is 1/6th of the potential and they are additive, multiply 6 for total v at centeris this correct solution? U is simple enough to do, simply multiply by -q. What is the methodology for solving part 3?