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Homework Help: I need help with a couple

  1. Jun 6, 2008 #1
    1. The problem statement, all variables and given/known data

    A person in a rowboat crosses a river which flows with 2.147 km/hr. The person rows with maximum velocity of 6.835 km/hr relative to the water (measured while rowing on a still lake) and wants to reach the opposite shore directly across from the start point - along a line at 90 degrees with respect to the river shore . At what angle with respect to this line does the person have to point the boat (sheet 15 to 16")? Indicate with a negative (positive) sign whether the boat has to be pointed upstream (downstream).
    2. Relevant equations

    3. The attempt at a solution

    I'm not sure how to solve this, but i used the vector decomposition, 43.39 degree . . . i used the forumula [cos(data) = Ax/A]

    Please anyone, help me out asap thank you so much...i need help urgently!!!
    Last edited: Jun 6, 2008
  2. jcsd
  3. Jun 6, 2008 #2
    Your answer and formula don't make sense to me, could you explain them? Draw a diagram of the situation, putting all known values and directions on it, then try again (it should look like a triangle).

    Vector decomposition should work, you want the the boat to travel upstream (or downstream) at a rate equal and opposite to the river flow, so that the sideways velocity components cancel each other out. Thus you know what the opposite will be and you already know the hypotenuse. From that you can find the angle and also the component of velocity across the stream.
    Last edited: Jun 6, 2008
  4. Jun 6, 2008 #3


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    Welcome to PF!

    Hi totororain ! Welcome to PF! :smile:

    Sorry, but your answer and formula don't make sense to me either.

    You need to show us exactly how you got to 43.39 … then we can see how to help you! :smile:
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