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**The potential difference necessary to accelerate an He+ ion....?**

## Homework Statement

"What potential difference is needed to accelerate a He+ ion (charge +e, mass 4u) from rest to a speed of 1.2×10^6 m/s?"

## Homework Equations

K_f + q*V_f = K_i + q*V_i

## The Attempt at a Solution

I figure that:

q = 1.6*10^-19 for the charge of an electron I believe...?

I started off thinking these were somehow true:

V_f = (1/2) m*vf^2

V_i = (1/2) m*vi^2

but now I realize that's just silly, and they both equal K....which is the kinetic energy, sure...but I still have *no* idea what the V's are going to be!

I'm honestly kind of banging my head against the book here...it's not really teaching me what I need to do this problem in any reasonably understandable way. Can anyone help out with this?