Another problem I'm struggling with this one I don't have a clue where to start. Any hints to a starting point would be greatly appreciated. A charge of -4.00uC is fixed in place. From a horizontal distance of 55.0cm a particle of mass 2.50 x 10^-3 kg and charge -3.00uC is fires with an intial speed of 15.0m/s directly toward the fixed charge. How far does the particle travel before it stops and begins to return back?