Answer:
8.75 fm
Explanation:
We use this expression
[tex]E=\frac{Ze*(2e)}{4\pi \epsilon_{0} *d}[/tex]
Which is derived from conservation of energy. E is the kinetic energy. d is the distance to find, Ze and 2e are the charges of the gold nucleus and alpha particle respectively. [tex]\frac{1}{4\pi \epsilon_{0} }[/tex] is the coulomb constant which is 9*10^9. Converting the energy to Joules
[tex]13 MeV*\frac{1 J}{6.24*10^{12}MeV}=2.08*10^{-12} J[/tex]
So, solving for distance (having all units in international system, distance ends up in meters)
[tex]d=\frac{9*10^9 *79*2*(1.6*10^{-19})^2}{2.08*10^{-12}} = 8.75*10^{-15} m[/tex]
In fermi:
[tex]8.75*10^{-15} m*\frac{10^{15} fm}{1 m}=8.75 fm[/tex]