Geometric Vectors Homework: River, Motor Boat, Marina

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Homework Statement



A river is 2 km wide and flows at 6 km/h. A motor boat that has a speed of
20 km/h in still water heads out from one bank perpendicular to the current.
A marina lies directly across the river on the opposite bank. Use Geometric
Vectors to solve this problem.

a. How far downstream from the marina will the boat reach the other bank? (Answer: 0.6 km)
b. How long will it take? (Answer: 6 min)

Homework Equations



The sine and cosine laws.

The Attempt at a Solution



Here's what I've done so far, I drew the diagram to the problem. I'm not sure if it's correct or not:

t5q87r.png


And now, I don't know what to do to answer the questions.
 
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I don't think the diagram is correct. The boat at 20km/h sets out horizontally (perpendicular to the current BUT since the current is pushing it down, the boat gets displaced diagonally. The boat will still reach the other side, but not in a straight line therefore missing the marina. That is why the first question asks how far DOWNSTREAM from the marina does the boat reach the other bank.
 
There are two things I don't understand about this problem. First, when finding the nth root of a number, there should in theory be n solutions. However, the formula produces n+1 roots. Here is how. The first root is simply ##\left(r\right)^{\left(\frac{1}{n}\right)}##. Then you multiply this first root by n additional expressions given by the formula, as you go through k=0,1,...n-1. So you end up with n+1 roots, which cannot be correct. Let me illustrate what I mean. For this...

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