Potential Difference and Kinetic Energy

[aimeemarie]

Hello out there! I am having trouble figuring out how to set this up:

A helium nucleus (charge +2e) moves through a potential difference V = −0.70 kV. Its initial kinetic energy is 3.80 10-16 J. What is its final kinetic energy?

I feel like I should be using 1/2 mv^2=qV or E=qv. I feel like maybe I am close but I am getting lost. Can anyone help explain this please??

 

[Delphi51]

Welcome to PF!

Just use E=qv. You aren't asked for velocity. Remember E=qv will be added onto the initial energy.

 

[Apphysicist]

Be sure to keep track of your negative signs.
Given you have a negative charge moving through a net negative potential difference...visualize: your nucleus moves from 0.7V (+) to 0V (-). Is it going to slow down (lose kinetic energy) or speed up (gain energy, the field associated with that voltage doing work on it) as it moves through that difference?

 

[aimeemarie]

I can't believe I didn't think to add them together, thank you :)