[tex]Dane:\\q_1 = q_2 = q = 2 \ C\\F = 90 \ C\\k = 9\cdot10^{9}\frac{Nm^{2}}{C^{2}}\\szukane:\\r = ?\\\\Rozwiazanie\\\\Korzystamy \ z \ prawa \ Coulomba\\\\F = k\cdot\frac{q_1 \cdot q_2}{r^{2}}\\\\q_1 = q_2 = q = 2 \ C, \ czyli:\\\\F = \frac{k\cdot q^{2}}{r^{2}} \ \ \rightarrow \ \ r^{2} = \frac{k\cdot q^{2}}{F}\\\\r = \sqrt{\frac{k\cdot q^{2}}{F}}\\\\r =\sqrt{\frac{9\cdot10^{9}\frac{Nm^{2}}{C^{2}}\cdot(2 \ C)^{2}}{90 \ N}}\\\\r =\sqrt{\frac{9\cdot10^{9}\cdot4}{90}} \ m\\\\r = \sqrt{4\cdot10^{8}} \ m[/tex]
[tex]\boxed{r = 2\cdot10^{4} \ m =20 \ 000 \ m = 20 \ km}[/tex]
