posted by Leah .
An incident X-ray photon of wavelength 0.2800nm is scattered from an electron that is initially at rest. The photon is scattered at an angle of 180.0 degrees and has a wavelength of 0.2849nm. Use the conservation of linear momentum to find the momentum gained by the electron.
I have no idea how to do it!PLEASE HELP!!!
Since the photon reversed, the electron must have gained twice that momentum.