A 33uC point charge is placed 36cm from an identical 33uC charge. A -2.5uC charge is moved from point a to point b in the figure:
The Attempt at a Solution
I found Ui by using above equation for each r from the -2.5uC charge and found the difference.
Repeated for Uf when charge is moved from a->b.
Uf-Ui = 1.74J, but MP says this is incorrect. What am I missing?