# Homework Help: Proton release inside a parallel capacitor Find velocity

1. Feb 5, 2012

### conov3

1. The problem statement, all variables and given/known data

The electric field strength is 47100 N/C inside a parallel-plate capacitor with 8.60 mm spacing. A proton is released from rest at the positive plate. What is the speed of the proton (in m/s) when it reaches the negative plate?

2. Relevant equations
Vf=√(-2U/m) I think?
ΔU=-.5eEd

3. The attempt at a solution

I tried using that equation to find ΔU=-3.768*10^-15
then plugged it in seem to have the wrong final answer though

Last edited by a moderator: Feb 5, 2012
2. Feb 5, 2012

### tiny-tim

welcome to pf!

hi conov3! welcome to pf!
why .5 ?

3. Feb 5, 2012

### conov3

Thank you! I figured since I am in a college level physics, I might as well try to get some help if I need it! ha

Using my Physics book.. it says ΔU=Uf-Ui= (Uo+ (-e)Ed)-(Uo+(-e)E(d/2)
Then under that it says =-1/2eEd

I am confused about it also and am really unsure.

4. Feb 5, 2012

### tiny-tim

i don't understand that … it doesn't seem to fit the question