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Amplitude of the spring motion

  1. Feb 7, 2009 #1
    A 0.38 kg mass is attached to a spring and executes simple harmonic motion with a period
    of 0.08 s. The total energy of the system is 1.9 J. Find:

    a) the force constant of the spring. Answer in units of N/m.
    b) the amplitude of the motion. Answer in units of m.

    For a, I got 2341.655 N/m by using the formula k= (T^2/4pi^2m)

    but how do I solve for b?

    And here is another question:

    A 1.02 kg mass is attached to a horizontal spring. The spring is initially stretched by 0.0478 m and the mass is released from rest there. After 0.507 s, the speed of the mass is zero (for the first time after being released). What is the maximum speed of the mass? Answer in units of m/s.

    I'm so lost in this questions because it is really confusing.
  2. jcsd
  3. Feb 7, 2009 #2
    Assuming that there is no friction, the total energy is constant. Do you have any equations, or can you form one, that relates the total energy (the only given datum that you have yet to use) to the amplitude?
  4. Feb 7, 2009 #3
    Nope, that's what I've been looking for till now. I'm doing a research on HOW to relate those equations...What about my other problems? and btw, this is an AP Physics course
  5. Feb 7, 2009 #4
    I guess you are supposed to derive the equation then? It's such a simple equation, but the derivation may take you some time.

    Hint: What are the equations for K(t) and U(t), where K(t) and U(t) are the kinetic and potential energies of the system for some time t? How are these quantities related to the total energy? :wink:
  6. Feb 7, 2009 #5
    are there any other people want to help me here??? :frown:
  7. Feb 7, 2009 #6
    At what point of the oscillation would the speed of the mass equal zero? What term in regard to distance does this correspond to? How is this distance related to the initial displacement that is given?

    You asked for help, but I have only asked you more questions. =) The problem should become clearer when you answer these questions.
  8. Feb 7, 2009 #7
    You don't like my help? Perhaps, you haven't thought about the problem enough. Physics isn't automatic.

    I'll shall refrain from further assistance. Btw, welcome to the Physicsforums.
  9. Feb 8, 2009 #8
    okay okay...anyways, I got the answer for B in the first questions. But I still can't figure out the answer for the second one...my friend told me to put it into the equation:
    1/2 K x^2 = 1/2 mv^2

    and solve for v but I didn't get the answer right...any suggestions??
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