Question

A –4.0-µC charge is located 0.45 m to the left of a +6.0-µC charge. What is the magnitude and direction (to the right or to the left) of the electrostatic force on the positive charge?

Answer 1

You have to use the electrostatic Coulomb's law :

\[E=k _{e}(q _{1}q _{2}/r ^{2})\]

with \[k _{e}=8,98.10^{9} N.m ^{2}.C ^{-2}\]
For the direction, think about what happened when you put two opposite charges (or the two sides of a magnet) together.