elastic headon collisions?

Question

a 2.0-g particle moving at 8.0 m/s makes a perfectly elastic head-on collision with a restiing 1.0 -g object. find the speed of each particle after the collision and find the stationary speed of each particle after the collision if the stationary particle has a mass of 10g.

Answer 1

1 g stationary particle:
VCM = (M1V1(i)+M2V2(i))/(M1+M2) = 5.333
VRel(i) = V1(i)-V2(i) = 8
VRel(f) = -VRel(i) = -8
V1(f) = VCM+VRel(f)*M2/(M1+M2) = 2.667
V2(f) = VCM-VRel(f)*M1/(M1+M2) = 10.667
10 g stationary particle:
VCM = (M1V1(i)+M2V2(i))/(M1+M2) = 1.333
VRel(i) = V1(i)-V2(i) = 8
VRel(f) = -VRel(i) = -8
V1(f) = VCM+VRel(f)*M2/(M1+M2) =-5.333
V2(f) = VCM-VRel(f)*M1/(M1+M2) = 2.667