Answer:
209.53 N
Explanation:
To find the force on the third charge you use the Coulomb formula:
[tex]F=k\frac{q_1q_2}{r^2}[/tex]
k: Coulomb's constant = 8.98*10^9 Nm^2/C^2
The force on the third charge is the contribution of the force between the third charge and the other ones:
[tex]F=F_1+F_2[/tex]
By taking into account that the third charge is at the middle of the distance between charge 1 and charge 2 you have r = 0.12m/2 = 0.06m
Furthermore, you take into account that the first charge repels the third charge and the second charge attracts the third charge.
By replacing you have:
[tex]F=k\frac{q_1q_3}{r^2}+k\frac{q_2q_3}{r^2}\\\\F=\frac{k}{r^2}q_3[q_1+q_2]\\\\F=\frac{(8.98*10^9Nm^2/C^2)(4*10^{-6}C)}{(0.06m)^2}[8*10^{-6}C+13*10^{-6}C]\\\\F=209.53\ N[/tex]
Hence, the force between on the third charge is 209.53 N
