when to use relative velocity and when to use resulltant velocity concept?

1)Wind is blowing east and man makes his strokes perpendicular to waters surface....here we take resultant velocity
take a look at this question down here...it involves relative velocity of flag with respect to boat but why?

Question

when to use relative velocity and when to use resulltant velocity concept?

1)Wind is blowing east and man makes his strokes perpendicular to waters surface....here we take resultant velocity
take a look at this question down here...it involves relative velocity of flag with respect to boat but why?

anonymous · Answer

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anonymous · Answer

Hey its the same question you asked yesterday know?

fretje · Answer

we call this true wind, headwind and apparent wind, in the sailing sport.  For the question in the jpg file, the true wind is 72 km/h direction North East.  The headwind is 51km/h direction South (because the boat goes North), and apparent wind is the addition  (so resultant) of these two.
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resultant makes an apparent wind to the East of 51km/h, which I call a strong wester