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# relatvistic collision watch

1. Hi,

There's a type of problem and I'm not entirely sure how to do it so if I give an example can someone post a solution (not allowed know but I've already handed it in and want to know if I did it right and if not how to do it as my tutor isn't the best at explaining stuff...)

In the first instance a positron collides with a stationary electron to produce a particle with rest mass 1200MeV, would I be right in saying that the energy that the positron must be accelerated to is 1200MeV minus the rest energies of the electron and positron?

In the second instance both the electron and the positron are moving towards each other, would the energy of each then be 600MeV?

Thanks.
2. (Original post by natninja)
Hi,

There's a type of problem and I'm not entirely sure how to do it so if I give an example can someone post a solution (not allowed know but I've already handed it in and want to know if I did it right and if not how to do it as my tutor isn't the best at explaining stuff...)

In the first instance a positron collides with a stationary electron to produce a particle with rest mass 1200MeV, would I be right in saying that the energy that the positron must be accelerated to is 1200MeV minus the rest energies of the electron and positron?

In the second instance both the electron and the positron are moving towards each other, would the energy of each then be 600MeV?

Thanks.
I suck at relativistic kinematics, but the general approach seems to always be that the square of the four momenta before, and after is conserved. So do

and then depending on the problem/reference frame, set the appropriate three momenta to be zero, and equal & opposite etc, to solve for the relevant quantity.

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