1. The problem statement, all variables and given/known data A charged particle (either an electron or a proton) is moving rightward between two parallel charged plates separated by distance d = 2.20 mm. The charge on the left has a potential of -70V and the charge on the right has a potential of -50V. The particle is slowing from an initial speed of 91.0 km/s at the left plate. (a) Is the particle an electron or a proton? (b) What is its speed just as it reaches the plate at the right? 2. Relevant equations ? 3. The attempt at a solution I understand that the particle is a proton, but I have not the slightest clue as to what equation to use. Any ideas?