Answer:
[tex]r = 2.84 \times 10^{-14} m[/tex]
Explanation:
As per energy conservation we know that the electrostatic potential energy of the charge system is equal to the initial kinetic energy of the alpha particle
So here we can write it as
[tex]\frac{1}{2}mv^2 = \frac{k(2e)(ze)}{r}[/tex]
now we know that
[tex]m = 1.67 \times 10^{-27} kg[/tex]
[tex]e = 1.6 \times 10^{-19} C[/tex]
z = 79
here kinetic energy of the incident alpha particle is given as
[tex]KE = 6.4 \times 10^{-13} J[/tex]
now we have
[tex]6.4 \times 10^{-13} = \frac{(9\times 10^9)(1.6 \times 10^{-19})^2(79)}{r}[/tex]
now we have
[tex]r = 2.84 \times 10^{-14} m[/tex]