I'm completely stumped on three questions, please help... 1. Particle 1 of charge +1x10^-6C and particle 2 of charge -3.0x10^-6C are held at separation L=10.0cm on an x axis. If particle 3 of unknown charge q3 is to be located such that the net electrostatic force on it from particles 1 and 2 are sero, what must be the x and y coordinates of particle 3? I know I need to use Coulomb's law, but since I don't know the unknown charge, how do I begin? 2. For particles are fixed in place and have charges q1=q2 = +5e, q3 = +3e, and q4 = -12e. They are all at a distance d = 5.0x10^-6m. What is the magnitude of the net electric field at point P due to the particles? q4 | | q3 | | q1------P------q2 I found that q1=q2 = 5e/[(4piEnot)(d)] so total = 2xans. q3 = +3e/[(4piEnot)(d)] q4 = -12e/[(4piEnot)(d)] Do I just add it to get the net electric field or am I just not understanding the problem? 3. To charged particles -q = -3.0x10^-19C at x = -3.00m and q = 3.0x10^-19C at x = 3.00m. What are the magnitude and direction (relative to the positive direction of the x-axis) of the net electric field produced at point P at y = 4.00m? I found E to be 2[3.2x10^-19/(4piEnot(3.0)^2)]sin 90, but it's not giving me the answer... does it have anything to do with the 4.00m? If so, how do I incorporate it in? Thanks for taking the time to look at this!