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Non-intertial frame problem

  1. Mar 10, 2009 #1
    1. The problem statement, all variables and given/known data

    A particle of mass M is hanging from one end of a massless spring, while the other is attached to the ceiling of an elevator.

    The elevator then starts to move upwards at an acceleration equal to g/5.

    Which way does the equilibrium shift, and what is the magnitude of the shift?

    2. Relevant equations

    F=-kx, F=ma

    3. The attempt at a solution

    Equilibrium when not moving...

    F=-kx=mg, so x=-(mg/k)

    When moving...

    F=-kx=m(g+(g/5))

    x= -(mg/k) - (mg/5k)

    Where the magnitude of the shift is -(mg/5k), and the equilibrium would shift downwards.

    Is this correct? Im a bit confused because i though x was displacement from equilibrium.
     
  2. jcsd
  3. Mar 10, 2009 #2

    PhanthomJay

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    Gold Member

    Yes, that looks correct. The mass will displace downward an additional mg/5k units from it's initial at rest equilibrium position, and the mass will be in its new state of dynamic equilibrium (not moving with respect to the elevator, but accelerating with respect to the ground).
     
  4. Mar 10, 2009 #3
    Great, thanks.
     
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