# Homework Help: Charged Particles (Potential Energy)

1. Sep 28, 2015

### kilnvzol

1. The problem statement, all variables and given/known data
Figure 24-21 shows four pairs of charged particles with identical separations. (a) Rank the pairs according to their electric potential energy (that is, the energy of the two-particle system), greatest (most positive) first. (b) For each pair, if the separation between the particles is increased,does the potential energy of the pair increase or decrease?

2. Relevant equations
U = W = (kq1q2)/r
3. The attempt at a solution
For part a, I got the ranking 3,2,4,1 by subtracting the second particle from the first one. ie. (1) -2-(+6) = -8
For part b, I got 1,4 increase whereas 2,3 decrease from the equation.
I haven't gotten the answers to these but I want to make sure I'm right.
Thank you!

2. Sep 28, 2015

### SammyS

Staff Emeritus
Not correct.

Did you use the relevant equation ?

3. Sep 28, 2015

### kilnvzol

Would this be right?
a. 3=4>2=1
b. 3&4 decrease 1&2 increase

4. Sep 28, 2015

### SammyS

Staff Emeritus
That looks to be correct .

5. Sep 28, 2015

### kilnvzol

Thank you!

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