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Reviewed CSCA Physics question · Easy

Two point charges, q1 = +6.0 μC and q2 = -4.0 μC, are placed 0.30 m apart in vacuum. What is the magnitude of the electric force that q1 exerts on q2? (Use k = 9.0 × 10^9 N·m^2/C^2.)

  1. 2.4 N
  2. 4.8 N
  3. 7.2 N
  4. 9.6 N
Show the answer and explanation

Correct answer

A. 2.4 N

Principle or equation

Coulomb's law: F = k |q1 q2| / r^2.

Why this answer is correct

F = (9.0e9) * (6.0e-6) * (4.0e-6) / (0.30)^2 = (9.0e9 * 24e-12) / 0.09 = 216e-3 / 0.09 = 2.4 N.

Example

For two 1 μC charges 0.1 m apart, F = 9e9 * 1e-12 / 0.01 = 0.9 N.

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