Electric potential energy and point charges problem

[abeltyukov]

Hi,

Homework Statement

Two point charges 2.0 cm apart have an electric potential energy -149.9 µJ. The total charge is 28 nC. What are the two charges?

Homework Equations

U = (kqQ) / r

The Attempt at a Solution

U = -149.9 x 10^-6 = [(9 x 10^9)(28 x 10^-9 - q)(q)] / (0.02). Is that correct? I seem to get the wrong answer.


Thanks!

 

[Chi Meson]

This appears to be a simulateous equation problem. You don't know what either charge is, but you do know that the sum of both charges is 28 nC. (If I understand the problem correctly).

Since the PE is negative, that means one charge is + and the other is -. Therefore, how much more is the + charge's magnitude greater than that of the negative?

 

[m2003]

Hello,

Your attempt at solving this problem is correct, however, you may have made a calculation error. According to your equation, the correct answer should be q = 7.5 x 10^-9 C. It is possible that you may have made a mistake while converting units or calculating the values. I would suggest double-checking your calculations to ensure accuracy. Additionally, it may be helpful to write out all the steps in your calculation to identify any errors. Keep in mind that the charges should be opposite in sign since the potential energy is negative. I hope this helps. Good luck with your homework!