Phase constant of SHM

  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. gneill

    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. OK

    1

    Huh??
     
  5. gneill

    Staff: Mentor

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

    Staff: Mentor

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

    Staff: Mentor

    Have a gander:

    [​IMG]
     

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