Answer:
[tex]\Delta U=-1.2\times^{-15}J[/tex]
Explanation:
The formula for electric potential energy between 2 charges [tex]q_1[/tex] and [tex]q_2[/tex] separated a distance r is [tex]U=\frac{kq_1q_2}{r}[/tex], where [tex]k=8.99\times10^9Nm^2C^{-2}[/tex] is the Coulomb constant.
The initial electric potential energy [tex]U_i[/tex] is then 0J, since r is infinite.
The final electric potential energy is
[tex]U_f=\frac{k(7e)(-6e)}{r}=\frac{-42ke^2}{r}[/tex]
Where [tex]e=1.6\times10^{-19}C[/tex] is the elementary charge.
Substituting values we have:
[tex]U_f=-\frac{42(8.99\times10^9Nm^2C^{-2})(1.6\times10^{-19}C)^2}{(7.5\times10^{-12}m)}=-1.2\times^{-15}J[/tex]
So we finally have:
[tex]\Delta U=U_f-U_i=-1.2\times^{-15}J-0J=-1.2\times^{-15}J[/tex]
