If you ever want to move yourself to the centerofmass, you will have to know what the center-of-massvelocity is.
你若想要移动,在重心体系中,你就必须知道,重心速度是多少。
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The velocityof the centerofmass has not changed as seen from your frame of reference, because the velocityofcenter of mass is always the same, remember, because momentum is conserved.