Collision of Alpha particle with a Gold Nucleous

[lebprince]

Homework Statement

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). I got the right answer here <1.427e-19,0,0>

b) What is the initial momentum of the gold nucleus? I also got this right <0,0,0>

c) What is the final momentum of the alpha particle, long after it interacts with the gold nucleus? Am stuck on this part.

The Attempt at a Solution

i was able to solve parts a and b. for part C i tried getting 2 equations so i got Kf1+Kf2 = 1.52e-12 which is the given Kinetic energy from the problem changed to Joules, and i got P1f + P2f = 1.47e-19 , and i don't know what else do if am on the right track. any help would be appriciated thanks.

 

[lebprince]

Ok there is a question after part c asking me for the final momentum of the gold nucleus long after the interaction with the alpha particle. i got the answer for that which was 2 * p1i, p1i is the initial momentum of the alpha particle. so 2 * 1.427e-19. now for part C i tried using the momentum principle and set p1i + p2i = p1f + p2f since i have p1i and p2i and p2f i can find part c which p1f but am not getting the right answer any help?