Question

What is the force, in terms of Coulomb's constant, between two electrical charges of `12 C` and `-7 C` that are `4 m` apart?

Answer 1

`F = -21/4 * k * C^2/m^2`

Explanation:

We know Coulomb's law:
`F = k (q_1q_2)/(r^2)`
where `k` is Coulomb's constant. We plug in the values we are given for `q_1, q_2, and r` and get
`F = k (12 * -7)/(4^2)\ C^2/m^2 = -21/4 * k * C^2/m^2`

This deals with units properly. If we assume all units are SI, we can write this as `F = -5.25 k`, but that may not be exactly what the question is asking for.