(adsbygoogle = window.adsbygoogle || []).push({}); Problem:

A fisherman sets out upstream from Metaline Falls on the

Pend Oreille River in northwestern Washington State. His

small boat, powered by an outboard motor, travels at a

constant speed v in still water. The water flows at a lower

constant speed vw. He has traveled upstream for 2.00 km

when his ice chest falls out of the boat. He notices that

the chest is missing only after he has gone upstream for

another 15.0 minutes. At that point he turns around and

heads back downstream, all the time traveling at the same

speed relative to the water. He catches up with the floating

ice chest just as it is about to go over the falls at his

starting point. How fast is the river flowing? Solve this

problem in two ways.(a)First, use the Earth as a reference

frame. With respect to the Earth, the boat travels upstream

at speed v - v_{w}and downstream at v + v_{w}.(b)A

second much simpler and more elegant solution is obtained

by using the water as the reference frame. This approach

has important applications in many more complicated

problems; examples are calculating the motion of

rockets and satellites and analyzing the scattering of subatomic

particles from massive targets.

I had no problem solving(a), my doubts arise when solving(b).

I desire to know if the following considerations for (b) are right:

- When the boat is travelling upstream his speed relative to the water reference frame is v + v
_{w}or simply v?- When the boat is travelling downstream his velocity relative to the water reference frame is v - v
_{w}or simply v?- The chest is motionless relative to the water reference frame.

Thanks in advance for your help.

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# Homework Help: Relative motion and velocity

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