What is the Correct Setup for River Relative Velocity Homework?

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Homework Help Overview

The discussion revolves around a problem involving relative velocity in the context of two students canoeing on a river. They drop a bottle while paddling upstream and later retrieve it downstream, raising questions about the correct setup for analyzing their velocities relative to the water and the earth.

Discussion Character

  • Exploratory, Assumption checking, Problem interpretation

Approaches and Questions Raised

  • Participants discuss the setup of the problem and the equations related to the velocities of the canoe and the water. There are attempts to clarify the relationship between the distances traveled and the reference frames involved.

Discussion Status

Some participants have suggested alternative ways to determine the time without calculations, while others have expressed disagreement regarding the initial equations presented. The conversation indicates a mix of interpretations and approaches being explored.

Contextual Notes

There is mention of the distances of 2 km and 5 km being referenced to the earth, which raises questions about the assumptions made in the setup. The original poster's diagram is noted as a point of discussion.

Toranc3
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Homework Statement


Two students are canoeing on a river. While heading upstream, they accidentally drop an empty bottle overboard. They then continue paddling for 1 h, reaching a point 2 Km farther upstream. At this point they realize that the bottle is missing and, driven by ecological awareness, they turn around and head downstream. They catch up with and retrieve the bottle (which has been moving along with the current) 5 Km downstream from the turn-around point.

I am wondering if the setup in my picture is correct. I have my work on there.


Homework Equations





The Attempt at a Solution



Vc/w = velocity of the canoe relative to the water.
Vc/e= velocity of the canoe relative to the earth.
Vw/e= velocity of the water relative to the earth.

Vc/e=Vc/w + Vw/e
 
Last edited:
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There is an easy way to get t2 without any calculation. This allows to get the river velocity quickly, and afterwards the problem is easy to solve.

I disagree with your equations V1=Vc/w and V2=Vc/w. The 2 and 5km refer to earth.
 
mfb said:
There is an easy way to get t2 without any calculation. This allows to get the river velocity quickly, and afterwards the problem is easy to solve.

I disagree with your equations V1=Vc/w and V2=Vc/w. The 2 and 5km refer to earth.

Yeah I messed up. How would you go about getting the time without calculations? By the way I got it.
 
Last edited:
Consider the problem in the frame of the bottle.
 

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