What Factors Affect the Emission of a Photon by an Electron?

[NATSALANE]

an electron travels at 1 x 10⁶ m/s. when it hits a target, its speed decrease in half and a photo is released. find the phton's wavelength.

so far i know E _photon = (hc) / lamda

what about the speed? does the photons' energy same as kinetic energy of the electron which is just 1/2 mv ^2? if so, do i use the halved speed or the initial?

 

[nicksauce]

Apply conservation of energy:

E_electron_inital = E_electron_final + E_phton