Answer
The electron will have the greater speed when it collides.
Work Step by Step
The electric force on a charge q in an electric field E is given by qE. The charges on a proton and electron are equal in magnitude, so the forces they experience in this situation are equal. However, the electron, with its much smaller mass, will have a much greater acceleration, and be moving faster upon impact with the plate.
This problem may also be analyzed in terms of energy, and the same conclusion is reached.
