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Old 08-23-2012, 07:54 AM   #42
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Originally Posted by sureshs View Post
That is what I always thought and have done problems with it, till I came up with the example above (inelastic collision) when I was trying to see if toly was wrong. Can you tell me the fallacy in my argument (#32)?
The law of conservation of momentum

If the velocities of the particles are U1 and U2 before the interaction, and afterwards they are V1 and V2, then

M1U1 + M2U2 = M1V1 + M2V2 (1)

This law holds no matter how complicated the force is between particles.

M1 and M2 are constants, but U1, U2, V1, and V2 are not. They depend on an arbitrarily chosen coordinate system. If we change coordinate system, we have to rewrite equation (1), but physics of collision process would be the same.
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