A fisherman sets out upstream on a river. His small boat,powered by an outboard motor

Chapter 4, Problem 79

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A fisherman sets out upstream on a river. His small boat,powered by an outboard motor, travels at a constantspeed v in still water. The water flows at a lower constantspeed vw. The fisherman has traveled upstreamfor 2.00 km when his ice chest falls out of the boat. Henotices that the chest is missing only after he has goneupstream for another 15.0 min. At that point, he turnsaround and heads back downstream, all the time travelingat the same speed relative to the water. He catchesup with the floating ice chest just as he returns to hisstarting point. How fast is the river flowing? Solve thisproblem in two ways. (a) First, use the Earth as a referenceframe. With respect to the Earth, the boat travelsupstream at speed v 2 vw and downstream at v 1 vw.(b) A second much simpler and more elegant solutionis obtained by using the water as the reference frame.This approach has important applications in manymore complicated problems; examples are calculatingthe motion of rockets and satellites and analyzing thescattering of subatomic particles from massive targets.