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December 20, 2014

Homework Help: Math: Calculus - Vectors

Posted by Anonymous on Tuesday, February 19, 2008 at 10:29pm.

A boat travels at a speed of 5 m/s in still water. The boat moves directly across a river that is 70m wide. The water in the river flows at a speed of 2 m/s. How long does it take the boat to cross the river? In what direction is the boat headed when it starts the crossing.

Textbook Answer: 15.3 m/s, 66.4 degrees to shore


My answer: 14 seconds and 22 degrees from the shore.

This is what I did: I found the speed of the resultant by doing the Pythagorean (5.4 m/s),then found the distance of the resultant by "5/70 = 2/x (28m)" and then using the Pythagorean (75.4m), and then I found the time by doing "t = d/s". Then, I found the direction of the boat by using trig, "tanx = 2/5"

-------------MY QUESTION: What did I do wrong? And can you please help me fix my mistake?

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