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Homework Help: Non inertial FoR

  1. Feb 18, 2010 #1


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

    A light spring force const. k hands from ceiling of an accelerating lift with a block of mass m attached to its bottom end. Block is held stationary (in lift frame) with the string at its equilibrium length while the lift is accelerating at a rate Ag where A is between -1 and 1 (const.) At t=0 the block is released from rest allowing it to execute SHM. Denote X by distance of block from origin of intertial FoR and Xo its distance when the spring is at equil. length..

    write down eqn of motion of block in interial FoR..

    then more qs

    2. Relevant equations

    3. The attempt at a solution

    I think (Xo-X)'' + k/m(Xo-X) = g

    I know Xo'' = Ag

    but how do i solve this eqn of motion?

    help!?! Thanks
  2. jcsd
  3. Feb 18, 2010 #2


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    Homework Helper

    Your equation seems right (although I haven't checked for sign issues), but I'd approach the problem in a different way. You can easily find the equation of motion of the block in the accelerating frame; just consider the acceleration of gravity to be Ag+g. You can also find the equation of motion for Xo; it's accelerating constantly. Add them together and you get the equation of motion for the block.
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