Chapter 4, Problem 51CP

Two swimmers, Chris and Sarah, start together at the same point on the hank, of a wide stream that flows with a speed v. Both move at the same speed c (where c > v) relative to the water. Chris swims downstream a distance L and then upstream the same distance. Sarah swims so that her motion relative to the Earth is perpendicular to the hanks of the stream. She swims the distance L and then back the same distance, with both swimmers returning to the starting point. In terms of L, c, and v_, find the time intervals required (a) for Chris’s round trip and (b) for Sarah’s round trip. (c) Explain which swimmer returns first.