[Yusf]

I found this question in a tutorial video:
An alpha particle with kinetic energy equal to 11 mega electron volts is directed to a lead nucleus. How close will it get to the nucleus before the particle completely stops?

Well, how am I supposed to solve this question without knowing the distance of the point where it first had 11 MeV energy? I mean the distance of the point the particle was released with that kinetic energy.

Is the solution, he wrote "work done equals the potential energy at the point the alpha particle stops."
And goes k*q1*q2/R=kinetic energy and solves for R as the answer.
Isn't that true only if the particle is released from infinity?

My main point is that I need a two point yo calculate the electrical potential energy in reference to each other. But the second one is not mentioned. And they ask me to solve for first point.

[ebaines]

I think you are correct, but from a practical point of view any reasonable starting distance is essentially infinity. Try solving for initial distance of say, 1 meter and compare that to the result of initial distance = infinity and I think you'll find essentially no difference.