Answer:
[tex]r^2 = \frac{ 2 k \ Ze^2}{ 2m}[/tex]
Explanation:
For this exercise we must use the principle of conservation of energy
starting point. The proton very far from the nucleus
Em₀ = K = ½ m v²
final point. The point where the proton is stopped (v = 0)
Em_f = U = q V
where the potential is
V = k Ze / r²
Let us consider that all the charge of the nucleus is in the center, therefore r is the distance from this point to the proton that is approaching
Energy is conserved
Em₀ = Em_f
½ m v² = e ([tex]k \frac{Ze}{r^2}[/tex])
[tex]r^2 = \frac{ 2 k \ Ze^2}{ 2m}[/tex]
with this expression we can find the closest approach distance (r)