jika gaya coloumb yg timbul antara 2 muatan adalah 4 N,maka r adalah(muatannya +5C dan +8C) tolong jawab please

Mapel : Fisika
Kelas : IX SMP
Bab : Listrik dan Magnet

Pembahasan :
F = k . (Q1 . Q2)/r²
4 = (9 x 10^9) . (5 . 8)/r²
4r² = (9 x 10^9) (40)
4r² = 36 x 10^10
r² = 9 x 10^10
r = √[9 x 10^10]
r = 3 x 10^5 m

[tex]\displaystyle Q_1=+5\,\text{C}\\Q_2=+8\,\text{C}\\F=4\,\text{N}\\k=9\cdot10^{9}\,\text{Nm}^2/\text{C}^2\\\\r=?\\\\F=k\frac{Q_1Q_2}{r^2}\\4=9\cdot10^9\frac{5\cdot8}{r^2}\\r^2=9\cdot10^9\frac{5\cdot8}{4}\\r^2=9\cdot10^9\cdot10\\r^2=9\cdot10^{10}\\\boxed{\boxed{r=3\cdot10^5\,\text{m}}}[/tex]