- #1

pearbear21

- 8

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## Homework Statement

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.

## Homework Equations

F=(kqQ)/r

^{2}

## 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

^{-15}m.

so, kqQ[tex]\int[/tex]r

^{-2}dr=kqQ[-r

^{-1}]

evaluated from [tex]\infty[/tex] to 4X10

^{-15}m 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.