I am not 100% sure this is the best substackexchange to ask my question, but I ll have a try.

I found this example where they calculate the velocity of the arm of a crane. But there are some parts which are unclear. (marked with a discrete red question mark)

1) When calculating $V_{p,drag}$ why is there that negative sign

2)When calculating $V_{p,drag}$ why are they adding the unit vector K? I'd expect vector Y, because the little cabines rotation axis is the vector Y.

3) Same story when calculating $V_{P,rel}$ I'd expect: $$ -6.(0,5)j + 10,4.(0,5)i$$ The j vector because the length 6m is in the j-direction.

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