What is the force, in terms of Coulomb's constant, between two electrical charges of ##8 C## and ##-2 C## that are ##9 m ## apart?

This question simply requires : ##F =(kq_1q_2)/r^2##. The answer is requested in terms of Coulomb's constant, and is ##F =(k*8*-2)/9^2 N =(-16k)/81 N##.

Coulomb's Law gives the force between two charged particles, given the magnitudes of the charge on them and the distance between them.

Coulomb's constant, the ##k## in the equation, is ##9*10^9 Nm^2C^-2##, but in this case we have been asked to answer in terms of this constant, so we express the answer in terms of ##k##.