Homework Help: Speed of Proton (given electric potential difference)

1. Jun 24, 2008

bec2008

1. The problem statement, all variables and given/known data
A proton, initially at rest, is accelerated through an electric potential difference of 500V. What is the speed of the proton?

2. Relevant 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

3. 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!!

2. Jun 24, 2008

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?)

3. Jun 24, 2008

Staff: Mentor

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?

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