Two point charges of 5 microcoulomb and 5 microcoulomb are 0.3 m apart in air (k = 9 x 10^9 N m^2/C^2). Find the force between them.

Answer and explanation

Correct answer: C. 2.5 N

  1. Step 1: Coulomb's law: F = k q1 q2 / r^2, with q1 q2 = 25 x 10^-12 C^2.
  2. Step 2: F = 9 x 10^9 x 25 x 10^-12 / 0.09 = 2.5 N.
Answer
2.5 N.
Why not the others: '0.75 N' uses r instead of r^2 in the denominator; '0.83 N' uses 3r^2 instead of r^2; '25 N' makes a power-of-ten error when converting microcoulombs.

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