Compton Effect: Finding Recoil Velocity of Electron at 180 Degrees

[so09er]

[SOLVED] Compton Effect question

A 125 keV photon scatters from a free electron initially at rest. Find the recoil velocity of the electron if the photon scattering angle is 180 degrees. (Use energy and momentum conservation.)

Am lost at where to go on this problem, thanks for any help that can be provided.

 

[Dick]

How does the momentum of a photon relate to it's energy?

 

[so09er]

thanks for the help

 

[lowerlowerhk]

I am kinda lost as well:
I have

hv=cp+hv' => hv'=hv-cp
hv+mc^2=(m^2c^4+c^2p^2)^1/2 +hv'

I have tried to sub hv'=hv-cp into equation 2, but I stil can't find the momentum of electron. Are the equations wrong?

 

[Dick]

I am kinda lost as well:
I have

hv=cp+hv' => hv'=hv-cp
hv+mc^2=(m^2c^4+c^2p^2)^1/2 +hv'

I have tried to sub hv'=hv-cp into equation 2, but I stil can't find the momentum of electron. Are the equations wrong?

Why don't you clearly label what your variables mean and then express the problem in terms of conservation of momentum and energy?