Four 50-\mu {\rm{C}} charges are brought from far apart onto a line where they're spaced at 2.0-{\rm cm} intervals. How much work does it take to assemble this charge distribution?

Answer 1

I answered a very similar question earlier today... only the separation distance was different. Use the same method, and the formula derived there:

http://www.jiskha.com/display.cgi?id=1265240265