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Homework Help: Hanging Mass on Spring

  1. Mar 2, 2012 #1
    1. The problem statement, all variables and given/known data
    A spring with spring constant k = 50 N/m and unstretched length of L is attached to the ceiling. A block of mass m = 1.5 kg is hung gently on the end of the spring. How far does the spring stretch?

    2. Relevant equations
    PEspring=0.5kx2
    Fspring=-kx

    3. The attempt at a solution
    When the mass hangs at rest at its lowest point where the spring is stretched the furthest, its weight is exerting a force of 14.7 N on the spring. Likewise, the spring should be exerting that same force on the mass, but plugging that into the force equation by dividing 14.7 by 50 gives an x value of 0.29 m, but this is incorrect. I must be overlooking something since I know I probably have to use the potential energy equation too. Any know what I'm doing wrong?
     
  2. jcsd
  3. Mar 2, 2012 #2

    gneill

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    Staff: Mentor

    Are there any particular units that they want the result expressed in? The force balance approach should be correct.
     
  4. Mar 2, 2012 #3
    Oh, apparently I was right, it was the significant figures that were saying it was wrong. Thanks anyway!
     
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