What speed must an electron have if its momentum is to be the same as that of an x-ray photon with a wavelength of 0.30?

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