You have a boat that is capable of moving at 10.4 m/s through still water. You wish to cross a river that flows due west at 2.8 m/s. At what numerical compass heading must you pilot your boat so that you will reach a destination that is due south of your current position?

Answer 1

well, you have to go upstream at an angle of arcSin(2.8/10.4) from the normal. Draw the figure, and think out why this is so.

Answer 2

-2.8 + Vb = -10.4i.
Vb = 2.8 - 10.4i. = 10.8m/s[-74.9o] = 74.9o S. of E. = 15.1o E. of S.