Two large parallel copper plates are 5.0 cm apart.  One is uniformly positively charged while the other is uniformly negatively charged resulting in a  uniform electric field between that is perpendicular to the plates and points from the positive plate to the negative plate. An electron is released from the negative plate at the same time that a proton is released from the positive plate.  Neglect the force of the particles on each other and find their distance from the postive plate when they pass each other.  (Does it surprise you that you need not know the electric field to solve this problem?)