Calculate the electrostatic force of attraction between two point charges of +2.0 μC and -4.0 μC separated by a distance of 0.20 m in a vacuum. (Coulomb constant k = 9.0 × 10⁹ N·m²/C²)
Answer and explanation
Correct answer: B. 1.8 N
- Step 1: State Coulomb's law: F = k |q1 q2| / r². Step 2. Substitute charges and distance: F = (9.0 × 10⁹ × 2.0 × 10⁻⁶ × 4.0 × 10⁻⁶) / (0.20)². Step 3. Calculate: F = (9.0 × 10⁹ × 8.0 × 10⁻¹²) / 0.04 = 0.072 / 0.04 = 1.8 N. Answer: 1.8 N. Why not the others: 3.6 N forgets to square the distance; 0.9 N halves the product; 7.2 N is an arithmetic order-of-magnitude error.
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