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Homework Help: Work/spring question

  1. Oct 14, 2008 #1
    1. The problem statement, all variables and given/known data
    An elevator cable breaks when a 760 kg elevator is 29 m above the top of a huge spring (k = 8.00 × 104 N/m) at the bottom of the shaft.
    (a) Calculate the work done by gravity on the elevator before it hits the spring.

    (b) Calculate the speed of the elevator just before striking the spring.

    (c) Calculate the amount the spring compresses (note that here work is done by both the spring and gravity).

    2. Relevant equations

    3. The attempt at a solution
    I got 215992 J for a, 23.8 m/s for b, and I need help with c. Thanks!
  2. jcsd
  3. Oct 14, 2008 #2


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    Homework Helper

    OK. What is the formula for Work done by the spring?

    It will involve a "distance", and the problem is telling you to include that additional potential energy in addition to the kinetic energy to determine the total depression.
  4. Oct 14, 2008 #3
    I took -215992 J = .5(-8.0x10^4)(d^2) and got 2.32 m which is not correct according to webassign.
  5. Oct 14, 2008 #4
    I figured it out ;)
  6. Oct 14, 2008 #5


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    Homework Helper

    Don't you also need the m*g*d term too?

    I presume this is the correction you discovered?
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