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Homework Help: Simple Vector Problem

  1. Sep 7, 2009 #1
    1. The problem statement, all variables and given/known data
    A child walks due east on the deck of a ship at 1 miles per hour.
    The ship is moving north at a speed of 4 miles per hour.

    Find the speed and direction of the child relative to the surface of the water.

    2. Relevant equations

    3. The attempt at a solution
    I've already found the magnitude. But now I can't find the direction.

    They want:

    "The angle of the direction from the north = "

    What does that mean? I've solved it using the inverse tangent for both angles of the triangle and apparently neither is right. So maybe it's even simpler than I think?
  2. jcsd
  3. Sep 7, 2009 #2


    Staff: Mentor

    What did you get for the angle relative to north? It should be somewhere between 10 and 20 degrees east of north.
  4. Sep 7, 2009 #3
    I got 14.03624347...in radians .2449786631(exact enough for you?:tongue2:)....does that sound about right?
  5. Sep 7, 2009 #4


    Staff: Mentor

    Your first value agrees with mine. I didn't calculate it in radians.
  6. Sep 7, 2009 #5
    Okay, cool. Thanks Mark, for all the help this morning(it's 2:30 here in Ohio). I can now begin my Materials and Energy Balances homework!
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