The momentum of the x-ray photon is p = h/lambda . Lambda is the wavelength (0.30nm=3x10^(-9)m) and h is Planck's constant,(h=6.62607004 × 10-34 m2 kg / s).The momentum is: 2.2 x 10^(-25).
The momentum can be calculated also as: p=mv, where m is the mass of the electron and v is the speed.
So v=p/m,p is known,and also the mass of the electron (m=9.10938356 × 10-31 kilograms).
v=2.2 x 10^(-25)/9.10938356 × 10-31 kilograms=0.24 x 10^6 m/s
