Is Electrostatic Potential Energy Always Equal to Work Done by Discrete Charges?

[jaejoon89]

I'm trying to figure out the following question

Which of the following is false?

1) The total work for a a collection of discreet charges is the system's electrostatic potential energy
2) The potential energy for a pair of bodies with positive charges is positive
3) The potential energy for a pair of bodies with opposite charges is positive
4) The potential energy for a pair of bodies with opposite charges is positive
5) The potential energy for a pair of bodies with negative charges is negative

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I know Vtot = V1 + V2 + ... and V = kq/r
so 2) and 5) seem to be true
For 1) W = - delta U so it's not exactly wrong (since the magnitudes are the same) but I don't think it can be considered right either
I'm not sure about 2) or 3)...

 

[alphysicist]

Hi jaejoon89,

I'm trying to figure out the following question

Which of the following is false?

1) The total work for a a collection of discreet charges is the system's electrostatic potential energy
2) The potential energy for a pair of bodies with positive charges is positive
3) The potential energy for a pair of bodies with opposite charges is positive
4) The potential energy for a pair of bodies with opposite charges is positive
5) The potential energy for a pair of bodies with negative charges is negative

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I know Vtot = V1 + V2 + ... and V = kq/r

That is the formula for potential, not potential energy. What is the formula for the potential energy of two point charges? Do you see how that will change your answers?