Two particles of masses m1 and m2 are moving in a straight line with velocities v1 and v2 respectively. If they collide elastically, what is the expression for the change in angular momentum about the center of mass?
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m1v1 + m2v2
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m1v1 - m2v2
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0
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m1v1 + m2v2 - (m1v1' + m2v2')