When two point charges are a distance d apart, the electric force that each one feels from the other has magnitude f. in order to make this force twice as strong, the distance would have to be changed

To solve this problem we will apply the concepts related to Coulomb's Law, for which electromagnetic force is defined as

k = Coulomb's Constant

= Magnitudes of the charges

r = Distance between the charges

From this equation and considering that the charges are constant, then we would have that the Force is inversely proportional to the distance of the bodies, that is,

If we then make the comparison between two Forces that proportion would become

We are looking for make this force twice as strong, then

Rearranging to find the final distance

As r = d,

Therefore the distance would have to be changed to

where are the vectors ?