A man can row a boat at 13m/s in still water. If the aims at crossing to the opposite bank of a river flowing 5m/s, at what angle to the bank of the river must he row the boat?

Answer 1

draw a picture

the cosine of the angle is ... 5 / 13

Answer 2

Vr = Vb - 5i = 13 = Resultant velocity.
Vb = 13 + 5i = 13.9 m/s[21o]. = Velocity of the boat.
Direction = 21deg. N. of E.