1. The problem statement, all variables and given/known data A particle of charge +q is a distance r away from a charged flat surface and experiences a force of magnitude F pulling it toward the surface. What is the magnitude of the force exerted on a particle of charge +q that is a distance 2r from the surface? 2. Relevant equations F=KQ1Q2/r^2 E=F/q E=Kq/r^2 3. The attempt at a solution The coulomb's formula seems to fit in i.e F=KQ1Q2/r^2 but I stopped solving it further since Q2 or the value of any other charge isn't mentioned in a question. Anyone please help me do this question? Thanks.