1. The problem statement, all variables and given/known data What energy alpha particle would be needed to just reach the surface of an Al nucleus if its radius is 4fm? *This problem is found in a section dealing with Rutherford's gold foil scattering experiment, so take it in that context. 2. Relevant equations F=(kqQ)/r2 3. The attempt at a solution I assume the book (Modern Physics by Tipler and Llewellyn ed. 5) wants this performed a classical manner, so I started by considering the energy of the particle as an integral of the coulombic force equation from r=[tex]\infty[/tex] to r=4X10-15m. so, kqQ[tex]\int[/tex]r-2dr=kqQ[-r-1] evaluated from [tex]\infty[/tex] to 4X10-15m gives a value of -1.4995992X10-12 Joules. This seems quite unreasonable as the repulsion seems intuitively large at such small distances and a joule is a small unit to begin with. What do you think of my method and answer? Do you feel there is a different way I should have approached the problem? At first, I tried finding the force to hold the alpha particle just on the surface of the Al nucleus, but after finding that force couldn't find a way to convert to energy correctly.