Question

Two charged particles Q1 and Q2 are a distance r apart with Q2=5Q1.Compare the forces they exert on one another when F1 is the force Q2 exerts on Q1 and F2 is the force Q1 exerts on Q2

Answer 1

a)F2=-5F1
b)F2=5F1
c)F2=F1
d)F2=-F1

I think it's d can anyone clarify

Answer 2

u r correct

Answer 3

Coulomb's law is F = k (q1q2)/r^2.

Just as with the law of universal gravitation the forces they exert on eachother are equal in magnitude, so we can rule out answers a and b.

The force they will exert on eachother (in terms of magnitude) is F = 5k (q1^2)/r^2, since q2 = 5q1. However, I would say that since force is a vector, the correct answer is d) F2 = -F1. The magnitudes are equal, but they are pointed in opposite directions (Newton's 3rd law).

Since q2 = 5q1, we also know that the force will be repulsive. This is an interesting 'feature' of Coulomb's law - if the magnitude of the force is positive, then it will be repulsive.