Answer:
P = M0 V / (1 - (V / C)^2)^1/2
Let V / C = X unless V is a close to the speed of light (10% or so)
(1 - x^2)^1/2 is a small quantity and can be ignored at small speeds.
(1 - [1 - (V/C)^2]^-1/2 = (V/C)^2 using the first terms of the binomial expansion
P2 / P1 = V2 / V1 * (X2 / X1)^2
For V<<C the effect is small and the momentum is merely doubled
