The current in the river is 1.0m/s.A woman swims 300m down stream and then back to her starting point without stopping.If she can swim $2.0m/s$ is still water,determine the time required for the round trip.

Question

$\begin{array}{1 1}400s\\100s\\200s\\300s\end{array} $

Answer 1

Answer : 400s

Down stream :

http://clay6.com/mpaimg/motion_plane.png

$\overrightarrow{V}_{PS}=\overrightarrow{V}_{PW}+\overrightarrow{V}_{WS}$

$\Rightarrow V_{PS}=2.0+1.0$

$\Rightarrow V_{PS}=3.0m/s$

$x=vt$

$\Rightarrow t=100s$

Upstream :

http://clay6.com/mpaimg/motion_plane1.png

$\overrightarrow{V}_{PS}=\overrightarrow{V}_{PW}+\overrightarrow{V}_{WS}$

$\Rightarrow V_{PS}=2.0+(-1.0)$

$\Rightarrow V_{PS}=1.0m/s$

$x=vt$

$\Rightarrow t=300s$

$\Rightarrow$ time =100+300=400s