Question

Two point charges Q1 =5πC and Q2 =8.5 πC are initially very for apart .They are them brought together, with a final separation of 3.5mm, How much work does it take to bring them together?

Answer 1

$$W=k\frac{q_1q_2}{r}\\W=(9\cdot10^9)\frac{(5\cdot10^{-12})(8.5\cdot10^{-12})}{(3.5\cdot10^{-3})}=1.1\cdot10^{-10}\ J$$