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Homework Help: Finding Amplitude-simple harmonic motion

  1. Nov 13, 2007 #1
    1. The problem statement, all variables and given/known data
    Simple harmonic motion problem.
    The number of daylight hours in a day is harmonic. Suppose that in a particular location, the shortest day of the year has 6.5 hours of daylight and the longest day of the year has 17.5 hours. Then, we can model its motion with the function N=Asin(bt)+C where t is expressed in days and A, B > 0. Find A and B, using 365 days for one year

    2. Relevant equations

    3. The attempt at a solution

    I found B to be .017214
    I found C to be 12
    I have no clue how to find the amplitude.. I've tried a million different ways.. submitted the answers.. and it keeps telling me its wrong.. so if anyone can help.. pllleeaassee do.. its due at midnight tonight and I have another problem exactly like this but with two different numbers in replace of the 6.5 and 17.5.
    How do you find amp??
    Last edited: Nov 13, 2007
  2. jcsd
  3. Nov 13, 2007 #2
    If the minimum is 6.5 and the maximum is 17.5, then what is the difference between these?

    That is your peak-to-peak amplitude.

    Your amplitude is simply half of this.
  4. Nov 13, 2007 #3
    I tried 12 and it's still wrong.. For the phase shift I put 12.. and that was right.. I don't know what to do?
  5. Nov 13, 2007 #4
    Where did you get 12 from?

    Have you sketched the graph?

    The amplitude is half of the difference between your max and min.
  6. Nov 13, 2007 #5

    I'm not very good at this stuff.. so I really don't know how to draw the graph.. i know how a sin wave goes.. but I'm just confused. I don't want you to do it for me.. i just want to know how to find amplitude.. but i'm confused because i understand what you are saying about the amplitude being half the difference between the max and min.. but it keeps telling me when i submit the answer that its wrong.
  7. Nov 13, 2007 #6

    Did you submit 6 hrs ?
  8. Nov 13, 2007 #7
    yes.. still wrong
  9. Nov 13, 2007 #8
    I'm sorry, (17.5 - 6.5)/2 = 5.5 Is it still wrong?
  10. Nov 13, 2007 #9
    yes.. i don't know if there is something wrong with the webwork or what.. i tried doing the same thing you suggested with the other numbers on the other problem i was given to do.. and it didnt work either..
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