If you have two charges q1 and q2, you can get the force between them F by multiplying them with the coulomb constant K (approximately 9 × 10^9) and then dividing that by the distance between them squared r^2.
q1 and q2 cannot be negative. Sometimes you’ll not be given a charge, and instead the problem will tell you that you have a proton or electron, both of them have the same charge (1.6 × 10^-19 C), but electrons have a negative charge.
q1 and q2 can be negative. The force is the same as if they were positive because -1 x -1 = 1
In this case yes, but if q1 was -20μC, q2 was 30μC, and r was 0.5m, then using -20μC as it is would make F equal to -21.6N which is just 21.6N of attraction force between the two charges.
If they are oppositely charged particles, I would expect that there is a force of attraction acting on them, yes.
But that if both are negative not one pos one neg like the previous commenter gave in their examples, so the true formula has an absolute value in the numerator: |q1Xq2|
