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Homework Help: Strecthing a wire - part 11

  1. Nov 23, 2007 #1
    1. The problem statement, all variables and given/known data

    I am in the vacuum of space. I carefully load a wire with a mass of 8kg, supporting the mass all the while with my hand. The wire stretches by 4.2 cm. What is the potential energy stored by the wire? What is the loss of potential energy of the mass?

    2. Relevant equations

    energy stored in the wire = work done in stretching the wire = 1/2 F.x
    gpe lost by mass = mgh

    3. The attempt at a solution

    energy stored in the wire = work done in stretching the wire = 1/2 F.x = 1/2 mgx = 1.65 J
    gpe lost by mass = mgh = 3.3 J

    The wire gains exactly half the energy lost by the mass. A curious result. The wire's c of g is also lower and hence the wire loses gpe. My hand is also lower than at the start and loses gpe. The wire was loaded so carefully that there was no perceptible rise in temperature of any part of the apparatus. Where has my missing energy gone?
  2. jcsd
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