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OSCILLATING my brain

  1. Aug 31, 2014 #1
    i know this problem is posted on this forum somwhere else but i cant quite understand thanks in advance

    1. The problem statement, all variables and given/known data

    A mass of 0.3 kg is suspended from a spring of stiffness 200 N m–1. If
    the mass is displaced by 10 mm from its equilibrium position and
    released, for the resulting vibration, calculate:

    the maximum velocity of the mass during the vibration

    2. Relevant equations

    F=kl



    3. The attempt at a solution

    so far i am thinking that i need to use hookes law as follows so i can get the amplitude
    F=k(l+x)

    F= mg = 0.3 kg x 9.81 = 2.94 N
    k = 200 Nm-1
    l = static spring reflection = 2.94/200 = 0.01
    x = displacement due to external force = 10mm

    so the amplitude would be l + x = 10.01mm?

    do i need to take into account the extra extension when attempting the solution or is it just f/k =l
    or do i need to use f/k = l + x to calculate the amplitude


    any help would be appriciated

    Thanks
     
  2. jcsd
  3. Aug 31, 2014 #2

    Simon Bridge

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    The oscillations are around the equilibrium position, not the unstretched length.
    Remember you have gravity as well as the string acting on the mass.

    I would use conservation of energy for this problem.
    For instance, at the top of the motion, the energy stored in the spring has been changed into gravitational potential energy.
     
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