# Homework Help: Help if Anybody has the time

1. Oct 16, 2008

### frangieh

1. The problem statement, all variables and given/known data

A swimmer wants to cross a river, from point A to point B, as shown in the figure. The distance d_1 (from A to C) is 200 m, the distance d_2 (from C to B) is 150 m and the speed v_r of the current in the river is 5 {km/hour}. Suppose that the swimmer's velocity relative to the water makes an angle of \theta = 45\;{degrees} with the line from A to C, as indicated in the figure.

To swim directly from A to B, what speed u_s, relative to the water, should the swimmer have?
1. The problem statement, all variables and given/known data

2. Relevant equations

3. The attempt at a solution

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2. Oct 16, 2008

### Andrew Mason

This is a vector problem. Do a vector diagram showing the velocity vector for the swimmer relative to water and the velocity vector for the water relative to land. How is the velocity vector of the swimmer relative to land related to these two vectors?

AM

3. Oct 16, 2008

### frangieh

A swimmer wants to cross a river, from point A to point B, as shown in the figure. The distance d_1 (from A to C) is 200 m, the distance d_2 (from C to B) is 150 m, and the speed v_r of the current in the river is 5 {km/hour}. Suppose that the swimmer's velocity relative to the water makes an angle of \theta = 45 degrees} with the line from A to C,

o swim directly from A to B, what speed u_s, relative to the water, should the swimmer have?

Vs =4.04 km/hour

because Vs =D1*vr(d1*sin(theta)+ d2*cos(theta))