You want to swim straight across a river that is 76m wide. You find that you can do this if you swim 28 degrees upstream at a constant rate of 1.7m/s relative to water. At what rate does the river flow? The angle is measure from the river bank (directly upstream is 0 degrees while directly across the river is 90 degrees.
physics - drwls, Monday, March 8, 2010 at 8:12am
The answer will not depend upon the width of the river. That number is there to confuse you.
To swim straight across, the swimmer's "relative to water" velocity component in the upstream direction must equal the river's speed downstream. Let the swimming angle relative to water, and the river bank, be A. Let the swimmer's velocity relative to water be v = 1.7 m/s.
v cos A = 1.7 cos 28 = V
V = 1.50 m/s