Speed of Proton (given electric potential difference)

[bec2008]

Homework Statement

A proton, initially at rest, is accelerated through an electric potential difference of 500V. What is the speed of the proton?

Homework Equations

V=k(q/r)
Solving for r: r=k(q/v)

v=d/t

known charge of a proton: 1.6E-19C
known value of k: 9E9Nm^2/C2

The Attempt at a Solution

I tried solving for r to get a distance.
r= (9E9Nm^2/C2)(1.6E-19C)/ 500V
r= 2.88E-12m

v=d/t
v= (2.88E-12m)/1 s
v= 2.88E-12 m/s

Our professor gave the answer as 3.1E5 m/s, but I cannot get to this answer. Any help would be greatly appreciated!

 

[rock.freak667]

Assume that all the work done by the source goes into increasing the speed of the proton (what sort of energy would it have when it moves?)

 

[Doc Al]

Homework Equations

V=k(q/r)
Solving for r: r=k(q/v)

That formula describes the potential from a point charge--not relevant here. (Further note that you are given potential difference, not potential.)

Hint: How does potential difference relate to energy?