Short Answer 
Coulomb’s Law describes the electrostatic force between two point charges, calculated using the formula F = k * (q1 * q2) / r¬≤. In a scenario with two charges, one attractive and one repulsive, the net force on charge A is zero, indicating that the forces cancel each other out.
Understanding Coulomb’s Law
Coulomb’s Law describes the electrostatic force between two point charges. It states that the force magnitude is directly proportional to the product of the charges and inversely proportional to the square of the distance separating them. The law can be represented by the equation:
- F = k * (q1 * q2) / r²
- Where F = force, k = constant (8.99E9 Nm²/kg²), q1 & q2 = charge magnitudes, r = distance between charges.
Calculating Forces between Charges
To determine the forces acting between the charges, substitute the values of the charges and distance into the equation. For two given charges:
- Charge A (qA) = 1.0E-9 C
- Charge B (qB) = -1.0E-9 C, distance (r) = 0.01 m, resulting in F(B on A) = +8.99E-5 N (attraction).
- Charge C (qC) = 4.0E-9 C, distance (r) = 0.02 m, resulting in F(C on A) = -8.99E-5 N (repulsion).
Finding the Net Force
The net force on charge A is calculated by summing the individual forces acting on it from charges B and C. Thus:
- Fnet (A) = F(B on A) + F(C on A)
- This yields Fnet (A) = 8.99E-5 N – 8.99E-5 N = 0.00 N, indicating no net force acting on charge A.