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Homework Help: Two masses attached to spring w/ pulley

  1. May 7, 2010 #1
    1. The problem statement, all variables and given/known data

    Two blocks, of masses M = 1.7 kg and 2M are connected to a spring of spring constant k = 180 N/m that has one end fixed, as shown in the figure below. The horizontal surface and the pulley are frictionless, and the pulley has negligible mass. The blocks are released from rest with the spring relaxed.

    http://img686.imageshack.us/img686/1376/stupidness.jpg [Broken]

    Uploaded with ImageShack.us

    (a) What is the combined kinetic energy of the two blocks when the hanging block has fallen a distance of 0.090 m?

    (b) What is the kinetic energy of the hanging block when it has fallen that 0.090 m?

    (c) What maximum distance does the hanging block fall before momentarily stopping?

    2. Relevant equations

    KEi + PEi = KEf + PEf

    Fs = kx

    3. The attempt at a solution

    I've tried to use the two masses as one system, and also have tried to separate them into two different systems. Neither way seems to be working for me, and I am just thoroughly confused. I would really like to believe that I only need a push in the correct direction.

    Thanks for any help offered! :D
    Last edited by a moderator: May 4, 2017
  2. jcsd
  3. May 7, 2010 #2


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    You should first determine if the speeds and distance travelled by each block are the same. Then using your conservation of energy equation, applied to the system, should give you the answer. Be sure to consider both gravitational and spring potential energies associated with spring-block system. Please show the values you are using in your equation.
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