# Alpha Particles and Momentum

1. Nov 27, 2008

### lebprince

1. The problem statement, all variables and given/known data

An alpha particle (a helium nucleus, containing 2 protons and 2 neutrons) starts out with kinetic energy of 9.5 MeV (9.5106 eV), and heads in the +x direction straight toward a gold nucleus (containing 79 protons and 118 neutrons). The particles are initially far apart, and the gold nucleus is initially at rest. Answer the following questions about the collision.

a)What is the initial momentum of the alpha particle? (You may assume its speed is small compared to the speed of light).

b)What is the final momentum of the alpha particle, long after it interacts with the gold nucleus?

c) What is the final momentum of the gold nucleus, long after it interacts with the alpha particle?

3. The attempt at a solution

i have solved the initial momentum for the gold nucleaus and got <0,0,0> which was true, and the y and z components of the final momentum of the gold nucleus are also 0's, but i couldnt find the x. i need some help with these 3 parts a,b,c Thanks

2. Nov 27, 2008

### Marco_84

i think you shold solve it in "routherford" way, not relativistically....

so try to think how to get the velocity from the kinetic energy, then use all the theorem you know, such as conservations of energy and momentum ;)

3. Nov 27, 2008

### lebprince

i know that k= 1/2 mv^2 and i have k given but how would i find m? is it the 4/avogadrosnumber?

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