Today we looked at how to find the force on a charge due to two or more charges by using Coulomb's Law.
http://hyperphysics.phy-astr.gsu.edu/hbase/electric/imgele/coulaw.gif
We worked on a problem in class with three charges on a line and then students got to work on the next HW assignment here .
If you missed class, or need a refresher on how to do these problems, check out this video.