[tex]dane:\\F = 5 \ N\\r = 20 \ cm = 0,2 \ m\\k = 9\cdot10^{9}\frac{Nm^{2}}{C^{2}}\\szukane:\\|q| = ?[/tex]
Rozwiązanie
Korzystamy z prawa Coulomba:
[tex]F = k\cdot\frac{|q_1\cdot q_2|}{r^{2}}\\\\|q_1| = |q_2| = |q|\\\\F = k\cdot\frac{q^{2}}{r^{2}} \ \ /\cdot r^{2}\\\\k\cdot q^{2}=F\cdot r^{2}} \ \ /:k\\\\q^{2} = \frac{F\cdot r^{2}}{k} \ \ |\sqrt{}\\\\|q| = r\sqrt{\frac{F}{k}}\\\\|q|= 0,2 \ m\cdot\sqrt{\frac{5 \ N}{9\cdot10^{9}\frac{Nm^{2}}{C^{2}}}}\\\\|q|=0,2\cdot\sqrt{\frac{5}{90\cdot10^{8}}} \ C\\\\|q| =0,2\cdot\sqrt{0,056}\cdot10^{-4} \ C \\\\|q| = 0,047\cdot10^{-4} \ C\\\\\boxed{|q| = 4,7\cdot10^{-6} \ C =4,7 \ \mu C}[/tex]