Pretty much, an object is moving at a certain velocity towards an "infinite" sheet with uniform charge density of sigma=4.4 nC/m^2. The object has a mass of m=62 ug and a charge of q=3.5 nC. It also has a velocity given in a vector v=(3.90i-4.80k) m/s. I am to find a bunch of stuff, but the first and foremost being the acceleration of the object. I've drawn the FBD. I'm not sure if I have the correct equation but I know that a=qE/m in general. However, I can't seem to find E. My teacher explained that when the distance r of an object is r<<length*width then to use E=sigma/(2*epsilon-not) (epsilon-not being the permittivity of space or 8.845*10^-12). But if I were to use that, I'd get E=248 N/C. Popping that into a=qE/m gives me the wrong answer however. Should I be accounting for the force the velocity has? Am I even using the right equation to find E? Using the answer I know for the acceleration, I can calculate that the E should be 74400. But then if I were to backtrack even further, that would mean that sigma would have to be some really off number. This is why I'm speculating that E is wrong. Unless I'm not accounting for another force to determine the acceleration. Ok, I'm rambling now. Any tips out there? Thanks in advance.