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Homework Help: 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


    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= 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

  2. jcsd
  3. Aug 31, 2014 #2

    Simon Bridge

    User Avatar
    Science Advisor
    Homework Helper

    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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