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Homework Help: Amplitude of Oscillation

  1. Dec 14, 2008 #1
    1. The problem statement, all variables and given/known data

    A 100 g ball is attached to a spring with spring constant 2.5 N/m oscillates horizontally on a frictionless table. Its velocity is 20 cm/s when x = -5.0 cm. What is the amplitude of the oscillation?

    2. Relevant equations

    x = Acos(ωt +φ )
    V= -ωAcos(ωt +φ )

    3. The attempt at a solution

    ω = Square root (k/m) = 5 rad/s
    -0.05 = Acos(ωt +φ )
    0.2 = -ωAcos(ωt +φ )

    Not sure how to solve for A
  2. jcsd
  3. Dec 14, 2008 #2
    To begin, you need to go back to your (relevant) equations. You have a differentiation mistake there that makes lit impossible to proceed correctly. Get this straight, and the solution for A should become evident using the Pythagorean trig identity.
  4. Dec 14, 2008 #3
    can I get φ clarified is it a constant? I know Acos(ωt+kx) is standard for traveling wave, however I am not certain of SHO for a spring what φ is.
  5. Dec 14, 2008 #4
    When an expression is written in that form, the implication is that phi is the phase angle, a constant. Evidently that was not explicitly stated, and it rarely is, but that is usually what is intended.
  6. Dec 14, 2008 #5


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    Homework Helper

    V= -ωAcos(ωt +φ )

    This expression is wrong. Check it.
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