# A question regarding electromagnetism

#### ichinose

Hi,
I encountered this problem:
A particle of charge Q and mass m is accelerated from rest through a potential difference V, attaining a kinetic energy K. What is the kinetic energy of a particle of charge 2Q and mass m/2 that is accelerated from rest through the same potential difference?

The correct answer is 2K; however, since KE = 1/2mv^2, and U=qV, shouldn't the kinetic energy be K?

Thanks!

Last edited:

#### oz93666

the second particle has twice the charge , so the force will be double , and since it's mass is half that of the first particle it will accelerate 4 times more quickly.

v2 (v squared) = 2as

The distance traveled by both particles is the same (s) the second particle has 4 times the acceleration.. so v squared is 4 times that of the first particle ,but the mass of the second particle is half ... so it's energy is only double that of the first....= 2K