Thank you for your reply. I'm looking at the solution of the problem you posted, but I'm having a hard time understanding it. I'll keep trying.
Edit: I hadn't seen posts after 60, now it's much more clear.
1. Problem
A boatman crosses a river of width ##D## from a point ##O##, looking to get to point ##A## on the opposite riverbank. Suppose that the flowrate is uniform with velocity of magnitude ##v_0##. The boat has a velocity ##\vec{v_1}## relative to the water, with constant magnitude, and it...