Ta có: $\overrightarrow {{F_3}} = \overrightarrow {{F_{13}}} + \overrightarrow {{F_{23}}} $
Do $\overrightarrow {{F_{13}}} \uparrow \uparrow \overrightarrow {{F_{23}}} $
$ \Rightarrow {F_3} = {F_{13}} + {F_{23}}$
Ta có: $\left\{ \begin{array}{l}{F_{13}} = k\frac{{\left| {{q_1}{q_3}} \right|}}{{A{C^2}}} = {9.10^9}\frac{{\left| {{{10}^{ - 7}}{{.4.10}^{ - 8}}} \right|}}{{0,{{04}^2}}} = 0,0225N\\{F_{23}} = k\frac{{\left| {{q_2}{q_3}} \right|}}{{B{C^2}}} = {9.10^9}\frac{{\left| {{{5.10}^{ - 8}}{{.4.10}^{ - 8}}} \right|}}{{0,{{01}^2}}} = 0,18N\end{array} \right.$
$ \Rightarrow {F_3} = 0,2025N$
