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paodealho
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Homework Statement
An unstable particle of mass M = m1 + m2 decays into two particles
of masses m1 and m2, releasing an amount of energy Q. Determine
the kinetic energies of the two particles in the CM frame. Given that
m1/m2 = 4, Q = 1 MeV, and that the unstable particle is moving in
the Lab with kinetic energy 2.25 MeV, find the maximum and minimum
Lab kinetic energies of the particle of mass m1.
Homework Equations
Conservation of Energy: [itex]\frac{1}{2}[/itex]MV2 = [itex]\frac{1}{2}[/itex]m1v12 + [itex]\frac{1}{2}[/itex]m2v22
Conservation of Momentum: MV = m1v1 + m2v2
The Attempt at a Solution
In the center of mass frame, the kinetic energy and momentum are zero initially. The particle decays and releases energy Q which becomes the kinetic energy of the two particles following decay in this frame.
So Q = [itex]\frac{1}{2}[/itex]m1v12 + [itex]\frac{1}{2}[/itex]m2v22 (1)
and m1v1 = m2v2
v1 = -m2/m1 * v2 (2)
Substituting (2) into (1):
Q = [itex]\frac{1}{2}[/itex][m1(-m2/m1 * v2)2 + m2v22]
After some algebra ...
T1 = [itex]\frac{1}{2}[/itex]m1v12 = Q * m2 / M
and
T2 = [itex]\frac{1}{2}[/itex]m2v22 = Q * m1 / M
The first part is all fine and dandy. I'm struggling with the second portion. I don't think I'm to consider the rest mass of the particles resulting from the decay... If all of the available energy becomes kinetic energy for m1 in the lab frame, wouldn't the maximum Kinetic energy just be 3.25 MeV for m1 ? (the textbook indicates otherwise: 3.20 MeV)
Following that line of logic, the minimum would just be zero but something doesn't seem right about that.
My apologies for the essay. I've tried all manner of shenanigans (conservation law manipulation) to find the min/max kinetic energies but have not succeeded. Am I just over-thinking this?
Thanks!