Suppose that the swimmer in the figure below has a swimming speed relative to the water of 0.45 m/s, while the speed of the current is 2.0 m/s. If it takes the swimmer 160 s to cross the river, how wide is the river?

Answer 1

As long as the swimmer is perpendicular to the river, the speed of the current doesn't really matter. The distance will always remain constant.
D = speed * time
D = 0.45 * 160
D = 72m