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Homework Help: Simple pendulums

  1. Apr 7, 2010 #1
    1. The problem statement, all variables and given/known data
    A 2.00-kg frictionless block is attached to an ideal spring with force constant 300 N/m. At t=0 the spring is neither stretched nor compressed and the block is moving in the negative direction at 12.0 m/s. Find the amplitude and the phase angle.

    2. Relevant equations
    [tex]\omega = \sqrt{\frac{k}{m}}[/tex]

    3. The attempt at a solution

    [tex]\omega = \sqrt{\frac{300}{2.00}} = 12.25[/tex]
    [tex]0 = A\cdot cos(\phi)[/tex]
    [tex]12.0 = -12.25 \cdot A \cdot sin(\phi)[/tex]

    How do I solve for something when there are two unknowns (phi and A)?
  2. jcsd
  3. Apr 7, 2010 #2
    Do I assume that A is non-zero, therefore making φ = Pi/2 radians?
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