Question

A boatman can row with a speed of 10km/h in still water. If the river flows at 5km/h, in which direction should boat man will row in water to reach a point on the other bank and also find the shortest possible time if the distance of both Bank in 1 kilometre

Answer 1

We need to find the angle made by the velocity vector of the boat with the velocity vector of the river.
To reach the opposite side of the Bank (from pt A to B) The resultant velocity must be perpendicular.

Solution is attached below.
Hope this helps.

Answer 2

Answer:

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