What Defines the Total Momentum in the Center of Mass Frame?

AI Thread Summary
The total momentum in the center-of-mass frame is defined as always being zero, which is a fundamental characteristic of this frame. The discussion also touches on the relationship between initial and final momentum vectors, emphasizing that they form pairs of equal magnitude and opposite direction. There is uncertainty regarding the term "initial index particle," with a request for clarification on its meaning. Additionally, it is noted that the center-of-mass frame does not always move at the same velocity as the initial index particle, particularly in inelastic collisions. Understanding these concepts is crucial for solving related physics problems.
Thefox14
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Homework Statement



A key concept about the center-of-mass frame is that

A. the total momentum in the center of mass frame is always zero.
B. both the initial and final momentum vectors form pairs of equal magnitude and opposite direction
C. this frame always moves at the same velocity as the initial index particle
D. (a) and (b)
E. (a) and (c)
F. all of the above

2. The attempt at a solution

Currently I think it's A, as that's one of the key things about this frame, but what makes me uncertain is I'm not sure what an initial index particle is. I'm also pretty sure it's not C as that would only be true for elastic collisions correct?
 
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Would someone be able to explain what an index particle is? Just knowing that would help a lot
 

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