I'm going on 10 years since I got my (physics) degree, but I haven't done much work besides conceptual stuff in that time and it shows. Anyway, I decided to crack open my Modern Physics book from school and start working my way through it. The first few problems were OK, but I just can't quite seem to get a handle on how to work through this one.(adsbygoogle = window.adsbygoogle || []).push({});

Here it is:

A beryillium atom (m[tex]\approx[/tex]8.00u) is moving in the positive x direction with a kinetic energy of 60.0 keV. It splits into 2 Helium atoms (m[tex]\approx[/tex]4.00u) with the release of 92.0 keV of Energy. Particle 1 is found to move at 30.0^{o}to the x-axis ([tex]\theta_{1}[/tex]). Using Conservation of Energy and Momentum (i.e., no coordinate transformations), find v_{1}, v_{2}, and [tex]\theta_{2}[/tex].

Conversion factor: [tex]1u = 9.3150 x 10^5 \frac{keV}{c^2}[/tex]

I think I've got the COE part set up correctly. Given that [tex]m_{1}=m_{2}\equiv m[/tex]

[tex]60.0 keV + 92.0 keV = \frac{1}{2}m(v^2_{1} + v^2_{2})[/tex]

By substituting known values, I get [tex]v^2_{1}+v^2_{2}=8.16x10^{-5} c^2[/tex]

The COM portion seems to be throwing me for a loop somehow. No matter how I set them up, when I substitute back into the COE equation, I end up with a really nasty looking quadratic equation. I know that the angle given [tex]\theta_{1}[/tex] and the relationship it implies for v_{1}to v_{1x}and v_{1y}must be the key, but I just can't seem to make it fit.

Thanks for any help you can offer,

Grogs

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# Homework Help: COM/COE Problem

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