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Annihilation

In annihilation of particles and antiparticles, why do we use the rest energy of the particles to equate to the photon energies, as surely you should account for the speed at which the particles are travelling at before?
You do I think? But in physics questions I think they water it down. Also are they asking you for the MINIMUM energy?
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mayjb
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Original post by crosssafley
You do I think? But in physics questions I think they water it down. Also are they asking you for the MINIMUM energy?


Oh of course it's the minimum energy, so do we just assume they're colliding... from rest? Thanks!
Original post by mayjb
Oh of course it's the minimum energy, so do we just assume they're colliding... from rest? Thanks!


Yes if it is the minimum you just take the rest energy however if they have kinetic energy you add that in as well.
Original post by mayjb
Oh of course it's the minimum energy, so do we just assume they're colliding... from rest? Thanks!


The mass is converted into energy and this quantity will be the minimum energy or the photons (the mass of one electron/positron is converted into one photon). Any initial kinetic energy that the particles have would also be transferred to the photon, however, this is unlikely to be asked as you will most likely have to assume they have no kinetic energy/collide at rest.

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