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Homework Help: Phase constant of SHM

  1. Oct 26, 2011 #1
    1. The problem statement, all variables and given/known data

    The displacement of a mass oscillating on a spring is given by x(t) = xmcos(ωt + ). If the initial displacement is zero and the initial velocity is in the negative x direction, then the phase constant is:

    2. Relevant equations



    3. The attempt at a solution

    How do I start? The book just tells me that the phase constant depends on displacement and velocity when t = 0, but doesn't say how.
     
  2. jcsd
  3. Oct 26, 2011 #2

    gneill

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    Staff: Mentor

    Sketch a cosine curve. What's its initial value? Where on the curve would match the initial condition of the spring and mass? What's (angular) the offset from zero?
     
  4. Oct 26, 2011 #3
    OK

    1

    Huh??
     
  5. Oct 26, 2011 #4

    gneill

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    Staff: Mentor

    Does the mass start at a maximum extension like the cosine function does?
     
  6. Oct 26, 2011 #5
    No, initial displacement is 0. So, I need to find where cosx equals 0?
     
  7. Oct 26, 2011 #6

    gneill

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    Staff: Mentor

    Not only that, but where it's going through zero and going negative, just like the mass' displacement.
     
  8. Nov 9, 2011 #7
    Still have no clue on this.
     
  9. Nov 9, 2011 #8

    gneill

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    Staff: Mentor

    Have a gander:

    attachment.php?attachmentid=40822&stc=1&d=1320887764.jpg
     

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