You want to swim straight across a river that is 76 m wide. You find that you can do this if you swim at an angle of θ = 28° from the upstream direction at a constant rate of 1.5 m/s relative to the water. At what rate does the river flow? The angle θ is measured from the river bank (directly upstream is θ = 0° while directly across the river is θ = 90°).
A) 1.3 m/s
B) 0.70 m/s
C) 1.6 m/s
D) 1.8 m/s

Question

Quizplus · Accepted Answer

The river flows at a rate of 1.3 m/s. This is because the swimmer's velocity relative to the water is 1.5 m/s, and the angle at which the swimmer is swimming is 28°. The velocity of the river is therefore 1.5 m/s * sin(28°) = 1.3 m/s.

You Want to Swim Straight Across a River That Is