Practice question

**Superposition principle** asserts net Coulomb force on charge equals vector sum of forces from each other charge independently, F_net = Σ F_i, where F_i = k q q_i/r_i² r̂_i. In equilateral triangle or square symmetry, components may cancel at centroid, producing equilibrium. Using Coulomb’s law: F = k (|q₁ q₂|/r²) . k = 9 × 10⁹ N·m²/C² , q₁ = 5 × 10⁻⁷ C , q₂ = -7 × 10⁻⁷ C , r = 1.5 m . |q₁ q₂| = 5 × 7 × 10⁻¹⁴ = 35 × 10⁻¹⁴ C² . r² = (1.5)² = 2.25 m² . F = 9 × 10⁹ × (35