動量問題[超難]

By conservation of momentom,
Initial momentom = final momentom
Initial momentom= 2x2+ 1x-4
=0Ns
Final momentom
A: 2x-2+1X4=0Ns

B:-1x2+1x2 =0Ns

C;2x0+1x0=0Ns

D:2x1+1x-2=0Ns

E:(2+1)x8/3=8Ns

P.S Since the original direction of A is +,they move toward each other, so the origianl direction of B is - .And velocity is vector ,so velocity of A is 2m/s while B is -4m/s.

Therefore, the answer is E.

Actually, All answers (A to E) are possible.
It can be cosidered by conservation of momentum and conservation of energy.
Answer A both obey conservation of momentum and conservation of energy.
Answers B to E obey conservation of momentum but mechanical energy is not conserved.
It doesn't mean that they are wrong, since energy can be converted to sound and heat in the collision.
But since B to E are equivalent, conserve in momentum but kinetic energy decrease, there is no way to tell which one is better among B to E. I would choose A as the correct answer.

2007-04-14 21:43:01 補充：
Sorry. I have misunderstanding about the question. The answer should be E just like the other person suggested.