To calculate the electric force between two charges, we can use Coulomb's law:
F = k * |q1 * q2| / r^2
where F is the electric force, k is the electrostatic constant (k ≈ 8.99 × 10^9 N m^2/C^2), q1 and q2 are the magnitudes of the charges, and r is the distance between the charges.
In this case, q1 = 0.0042 C, q2 = -0.0050 C, and r = 0.0030 m.
Substituting these values into the equation:
F = (8.99 × 10^9 N m^2/C^2) * |0.0042 C * (-0.0050 C)| / (0.0030 m)^2
F = (8.99 × 10^9 N m^2/C^2) * 0.000021 C^2 / 0.000009 m^2
F ≈ 1977.78 N
Therefore, the electric force between the two charges is approximately 1977.78 Newtons.