# Photon smashing electron

quietrain

## Homework Statement

A photon strikes an electron of mass m that is initially at rest, creating an electron-positron
pair. The photon is destroyed and the positron and two electrons move
off at equal speeds along the initial direction of the photon. The energy of the
photon was ?

## The Attempt at a Solution

are we suppose to use momentum conservation?

or kinetic energy conservation?

do we have to factor in relativistic effects?

but i have totally no idea at all how to get that

i think the final mass = 1.5 m ? where m = electron mass

because positron and electron pair = 0.5 m , then add in the other stationary electron so 1.5m ?

this is confusing . greatly appreciate any help thanks!

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