physics
posted by Cassie .
A point charge with charge q1 is held stationary at the origin. A second point charge with charge moves from the point (x1,0) to the point (x2,y2).
How much work is done by the electrostatic force on the moving point charge?
Express your answer in joules. Use k for Coulomb's constant ().

Compute how the distance from the origin changes. That would be from
r1 = x1 to
r2 = sqrt(x2^2 + y2^2)
The work done moving the charge is
k q1*q2/[(1/r2  1/r1]
You need to provide values for q2, q1, and the locations to compute the work in Joules. 
Why are the r's reciprocal??