Electric potential energy and point charges problem

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SUMMARY

The forum discussion centers on a physics problem involving two point charges separated by 2.0 cm with an electric potential energy of -149.9 µJ and a total charge of 28 nC. The equation used to calculate the potential energy is U = (kqQ) / r, where k is the Coulomb's constant. The user attempts to solve for the individual charges but encounters difficulties, indicating that the problem requires simultaneous equations due to the unknowns. The negative potential energy suggests one charge is positive and the other is negative, leading to a need for further analysis of their magnitudes.

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  • Understanding of electric potential energy and its formula (U = (kqQ) / r)
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abeltyukov
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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!
 
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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?
 

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