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Harmonic movement of a spring question

  1. Jan 8, 2009 #1
    i got a mass "m" which is stuck to a spring which is hanged from the sealing .
    k-the spring coefficient
    the formula for acceleration is

    a=-A*w^2*sin(wt+u)
    i need to calculate the force which the spring exerts of the mass in any given moment
    t=0 is when he was moved downward by distance A (amplitude) to some amplitude and released.

    my main question is why the phase angle "u" is pi/4 ??
     
  2. jcsd
  3. Jan 8, 2009 #2
    Your initial conditions gives these equations, from which you should be able to retrieve u:
    r(t)=Asin(wt+u)
    r(0)=A
     
  4. Jan 8, 2009 #3
    my main question is why the phase angle need to be pi/4 ??
    how do i count the phrase angle in this string situation
    just by viewing the location of the object.
     
  5. Jan 8, 2009 #4
    m is mass
    + is the point of balance
    what is the phase angle if we start counting from this position?
    +
    |
    |
    m
     
  6. Jan 8, 2009 #5
    Imagine the unit circle projected onto the y-axis, then pi/4 corresponds to 1, 0 and pi to 0 and -pi/4 to -1 as initial positions.
     
  7. Jan 9, 2009 #6
    i cant image what you say
    can you draw it??
     
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