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Homework Help: Springs, Kinetic Friction, and Distance help me please

  1. Feb 25, 2008 #1
    Springs, Kinetic Friction, and Distance....help me please

    1. In the figure below a 1.4 {\rm kg} block is held at rest against a spring with a force constant k = 740 {\rm N/m}. Initially, the spring is compressed a distance d. When the block is released, it slides across a surface that is frictionless except for a rough patch of width 5.0 {\rm cm} that has a coefficient of kinetic friction mu = 0.44.

    2. Questions: Find d such that the block's speed after crossing the rough patch is 2.3 {\rm m/s}. /b]

    [PLAIN][PLAIN]http://img84.imageshack.us/img84/1249/111it7.jpg [Broken]

    3. Relevant equations: Ok, I know how to apply the kinetic friction to the mass but how do I start this equation? What effect does the force of the spring have on the velocity and how does the defined distance work out? I really want to understand this but am afraid that conceptually it's hard for me to work out. Any pointers or all applicable equations would greatly be appreciated so I could get on with this. I have been doing Chemistry since 6am and my brain is just not tickin right now...

    I apologize if I messed up the template, this is my first post so I will hope to not make any mistakes again if i did this time.

    Also, my work as of right now for this problem consists of 2 pages front to back with writing all over, I really wouldn't know where to start and am so confused at this point that I could really use a push.
    1. The problem statement, all variables and given/known data

    2. Relevant equations

    3. The attempt at a solution
    1. The problem statement, all variables and given/known data

    2. Relevant equations

    3. The attempt at a solution
    Last edited by a moderator: May 3, 2017
  2. jcsd
  3. Feb 25, 2008 #2


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    Staff Emeritus
    Science Advisor

    Starting with 2.3 m/s speed of the block after it passes, compute the kinetic energy of the block.

    When the block passed over the rough surface, friction did work against the block, so some energy was lost. Determine the work done on the block. The kinetic energy of the block before it enountered the rough surface must be the sum of the KE after and the work done by friction.

    The kinetic energy of the block comes from the energy stored in the spring, which is related to the deflection of the spring and spring constant.
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