Question

Point A is at a potential of +250 V, and point B is at a potential of -150 V. An á-particle is a helium nucleus that contains two protons and two neutrons; the neutrons are electrically neutral. An á-particle starts from rest at A and accelerates toward B. When the á-particle arrives at B, what kinetic energy (in electron volts) does it have?

Answer 1

The charge is 2e and the voltage change is 400 V. Multiply them together for the kinetic energy gain.

You could also compute the final speed using the alpha particle mass, but they don't ask for that.