# Physics:Find the least value of 𝑢 needed for the yacht to safely enter the harbour.?

The entrance to a harbour is a channel of length 𝑎 which runs between two sandbanks a distance 𝑏 apart. The banks and the channel can be assumed to be rectangular. On this particular day, there is a current of constant speed 𝑣 flowing from one sandbank to the other. A yacht travelling at a constant speed relative to the water of 𝑢 wants to enter the harbour.

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- oldschoolLv 71 month ago
We know the yacht has to travel through the sand banks the distance √(a²+b²) at speed u before the current at speed v drives it off course distance b.

t = [√(a²+b²)]/u

But b = v*t and t = b/v

b/v = [√(a²+b²)]/u

u = v/b * [√(a²+b²)]

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- billrussell42Lv 71 month ago
what is 𝑢 ? it's not on the diagram or your text.

and what does θ indicate.

all of the question, not part of it....

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