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Homework Help: Energy considerations in strings

  1. Jan 16, 2010 #1
    1. The problem statement, all variables and given/known data
    The problem concerns a block(mass M) hanging from a light string attached to a fixed support, that is pulled down with a force of the block's weight that produces an extension of 'l'.

    2. Relevant equations

    The elastic P.E is half of (M*g*l).However the loss in gravitational P.E is (M*g*l), The question is where does the other half go?

    3. The attempt at a solution
    My guess is hysterisis as in rubber.
    Last edited: Jan 16, 2010
  2. jcsd
  3. Jan 16, 2010 #2


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    Where did you get this from? This is not the potential energy for a string that obeys hooke's law.
  4. Jan 16, 2010 #3
    The p.e is YAl^2/2L. However F=YAl/L. Here the maximum tension here is M*g as the block is supposed to hang in eqilibrium. Hence half of M*g*l. Most textbooks abbreviate it as half of max.tension multiplied into extension.

    As for the info it is from The Concepts Of Physics.
  5. Jan 17, 2010 #4


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    Ah my mistake, im quite rusty on this sort of stuff unfortunately. Hopefully someone else can help you here.
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