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amr55533
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Homework Statement
An alpha particle traveling with a kinetic energy of 5.5 MeV and a rest-mass of 3727.8 MeV/c^2 strikes a gold atom with a rest-mass of 183,476 MeV/c^2.
-The gold atom is initially at rest
-The alpha particle deflects perpendicular to the horizontal in the after state
Homework Equations
Conservation of Energy:
Ebefore=Eafter
Conservation of momentum:
Pbefore=Pafter
E^2=P^2c^2+(mc^2)^2
The Attempt at a Solution
Total Energy Before Collison:
Ebefore=E(α)+E(Au)=3727.8MeV+5.5MeV+183476MeV=187,209MeV
Momentum before (in x-direction):
E^2=p^2c^2+(mc^2)^2
==> (3727.8+5.5)^2=P^2c^2+(3727.8)^2
==> P=202.6 MeV/c
AFTER STATE:
Conservation of momentum:
in x: P(Au)cosθ=202.6MeV/c (1)
in y: P(Au)sinθ-P(α)=0 (2)
Conservation of Energy:
E(Au)=√(P(Au)^2+183476^2)
E(α)=√(P(α)^2+3727.8^2)
==> √(P(Au)^2+183476^2)+√(P(α)^2+3727.8^2)=187,209 MeV (3)
Solve the system of equations to find θ, P(Au), and P(α):
Solve (3) for P(α):
P(α)=√(1.36998E9-P(Au)^2)
Plug back into Eq. (2):
P(Au)sinθ=√(1.36998E9-P(Au)^2)
Solve (1) for θ:
θ=arccos(202.6/P(Au))
Plug into (2) and solve for Au:
P(Au)sin[arccos(202.6/P(Au))]=√(1.36998E9-P(Au)^2)
==> P(Au)=26,172.7 MeV/c
Solve for θ:
26,172.7cosθ=202.6
==> θ=89.56°
Solve for P(α):
26,172.7sin(89.56°)=P(α)
==> P(α)=26,171.9 MeV/c
However, when I plug these numbers back into equation (3) the solution doesn't come out right. I have been looking over this for hours and can't figure out where my error might be.
Thanks!