An electron starting from rest acquires 4.20 keV of kinetic energy in moving from point A to point B. How much kinetic energy would a proton acquire, starting from rest at B and moving to point A?

Question

Determine the ratio of their speeds at the end of their respective trajectories.

Answer 1

I assume that the energy comes from asn E field between A and B.
The force is proportional to charge and E so the force magnitude is equal (opposite sign though )
The distance is the same so the work done is the same.
So the kinetic energy is the same (1/2) m v^2
so
(1/2) Mproton Vproton^2 = (1/2) Melectron Velectron^2
so
Vproton^2/Velectron^2 = Melectron/Mproton