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Ocean Word Problem

  1. May 11, 2016 #1
    1. The problem statement, all variables and given/known data

    The water depth in a harbour is 21m at high tide and 11m at low tide. One cycle is completed approximately every 12 hrs.

    Find an equation.

    2. Relevant equations


    3. The attempt at a solution

    The answer to this problem is y = 5sin 30 (t-3) + 16

    A = (M - m) / 2
    = (21-11) / 2
    = 5

    C = (M+m) / 2
    = (21+11)/2
    =16

    Period is 12 hrs.
    K value would be 30 because 360 / 12.

    But I don't know why it is (t-3) I'm not sure where that came from.
     
  2. jcsd
  3. May 11, 2016 #2

    berkeman

    User Avatar

    Staff: Mentor

    Is there a little bit more to the problem statement? What times are high tide and low tide? You need to know those times in order to get the time part of your equation correct... :smile:
     
  4. May 11, 2016 #3

    Mark44

    Staff: Mentor

    How would the graph of ##y = 5\sin(30t) + 16## look in comparison to ##y = 5\sin(30(t - 3)) + 16##?
     
  5. May 11, 2016 #4
    Wouldn't the second graph be shifted 3 units to the right?
     
  6. May 11, 2016 #5

    Mark44

    Staff: Mentor

    Yes. So the point (0, 16) on the first graph is shifted to the right by 3 (hours?) is now at (3, 16).
     
  7. May 12, 2016 #6

    berkeman

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    Staff: Mentor

    Why is it shifted? What in the original problem statement helps you to figure out when low tide is? You cannot answer this schoolwork problem without that information. And our help is limited by the accuracy of what you post about the Problem Statement.

    EDIT -- Apologies, but this is a very straightforward problem if you post all of the question information.
     
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