A photon of frequency 5.00×1018Hz scatters from an initially stationary free electron. The scattered photon’s frequency is 4.88×1018Hz. Treating the electron non-relativistically, what is the speed of the electron immediately after the collision?
a) 7.2×106m/s
b) 1.3×107m/s
c) 9.4×106m/s
d) 4.2×106m/s