Electric field/charge woed problem

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Dx
A copper peny has a mass 3g. A total of 4 x 10^12 electrons are transferred from one neutral penny to another. If the lectrostatic force of attraction between the pennies is equal to the weight of a penny, what is the separatio between them?

what do i do here, i donno where to begin?

Dx :wink:
 

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Tom Mattson
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The problem pretty much tells you what to do. You are told the charge on each penny, so you should be able to set up the expression for the electric force between them (the separation r is unknown). You are also told the mass of a penny, so you should be able to calculate the weight.

Finally, you are told that the electric force is equal to the weight. Set them equal and solve for r.
 
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