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Question: 

A swimmer is capable of swimming 0.60 m/s in still water.

  1. If she aims her body directly across a 45-m-wide river whose current is 0.50 m/s, how far downstream (from a point opposite her starting point) will she land?
  2. How long will it take her to reach the other side?

Source: Giancoli, Douglas C., Physics: Principles with Applications, 7th Edition, 2014.

Quick Answer: 
  1. $75\textrm{ s}$
  2. $38\textrm{ m}$

Giancoli 7th Edition, Chapter 3, Problem 46

(2:24)

Chapter 3, Problem 46 is solved.

View sample solution

Comments

For part a, why do we use the current velocity and not the resultant velocity to solve how far downstream she will land?
Thanks!

Hi aheumangutman, "downstream" is the "x-direction" in the video. In order to know displacement in that direction (which is the "x-component" of the resultant displacement), we need to use the velocity along that direction. This is the "x-component" of the resultant velocity, but there's no need to do calculations for this "x-component" since the x-component is the speed of the current. In order to find the displacement along a certain direction, we need to know the velocity only along that direction.

Hope that helps,
Mr. Dychko