Swimming at 3.00 m/s relative to still water, a swimmer heads directly across a river of width 80 m. He arrives 50 m downstream from the point directly across the river from his starting point.

Question

Swimming at 3.00 m/s relative to still water, a swimmer heads directly across a river of width 80 m. He arrives 50 m downstream from the point directly across the river from his starting point. 
(a) What is the speed of the current in the river?

(b) At what angle relative to the line perpendicular to the shore should he head to arrive at a point directly opposite his starting point?

bobpursley · Answer

time to swim across: 80/3 seconds water velocity=50/(80/3) m/s head upstream arc tan 50/80