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Mar7-12, 05:01 AM
PF Gold
P: 4,745
Quote Quote by ENDLESSYOU View Post
When we dealing with questions like "S'-frame moves with respect to S-frame at a velocity u in x direction" then we also assume that "S-frame also moves with respect to S'-frame at a velocity -u in x direction"
Why this assumption is correct?
I think you are asking why the velocity changes sign, correct? Well, isn't it obvious if there is a relative speed between us and I see you moving east with respect to me, then you will see me moving west with respect to you? It really doesn't matter which one or both of us is actually moving, we're talking about relative speed. Doesn't this make sense to you?