Electric potential no clue and midterm in 2 and a half hours

[cemar.]

Homework Statement

A proton is fired from far away toward the nucleus of an iron atom. Iron is the element number 26 and the diameter of the nucleus is 9.0fm. What initial speed does the proton need to just reach the surface of the nucleus? Assume the nucleus remains at rest.

Homework Equations

Conservation of energy which would get reduced to Ki=Uf
U=kq1q2/r
kinematic equation
K = 1/2 m v^2
Do some thing with the element number 26... has 26 protons so make a field?

The Attempt at a Solution

Oh gosh. K this is completely wrong but ill just throw it out there for kicks.
Ki=Uf
Since i don't knwo what r is since its sperical and that confuses me... ill guess you use the distance on the surface of the nucleus?
1/2mv^2 = kq1q2/r
1/2 (1.67E-27) v^2 = 9E9 (1.6E-19) (26*1.6E-19) / 4.5fm
v = 350192

the answer is 3.99E7

Thank you!

 

[Doc Al]

1/2mv^2 = kq1q2/r
1/2 (1.67E-27) v^2 = 9E9 (1.6E-19) (26*1.6E-19) / 4.5fm

This is perfectly correct, just redo your arithmetic. (Change fm to standard units.)

 

[cemar.]

Seriously?!? thanks!
Im a mess! :S
You wouldn't happen to know and equation concerning the diameter of a wire with length and current and all that jazz would you??

 

[Doc Al]

You wouldn't happen to know and equation concerning the diameter of a wire with length and current and all that jazz would you??

Not sure what you're asking. If you post a complete problem, I can take a look.