Relative Motion: Sum or Difference of Vectors? - Sarahchichi

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Relative motion can be determined by either summing or subtracting vectors based on the context of the problem. To find the relative velocity, use the formula V_ab = V_a - V_b, where you assign a positive direction for clarity. There are no strict rules; the choice between sum or difference depends on the specific scenario and the chosen reference direction. The resulting sign of the relative velocity indicates the direction of motion. Understanding these principles is essential for accurately analyzing relative motion.
Sarahchichi
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hello, everybody.
I have a question about relative motion. I don't know how to determine whether it is sum of vectors or difference of vectors.
Vab=Va-Vb
Could you explain to me? When should use the sum of vectors and when should use the difference of vectors?

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Well, if you need the sum of 2 vectors you should add, if you need the difference you should subtract.

Your question is to general, you need to ask a specific question.
 
There's no strict rule . Take one direction to be positive , and Apply V_ab = V_a - V_b . Take V to be positive if it is in the direction which u took to be positive or take it as negative if it is in direction opposite to the one you took as positive. The final relative velocity will be positive or negative and thus will telll you , in which direction it is directed.

BJ
 

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