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Homework Help: Spring problems

  1. Dec 3, 2009 #1
    1. The problem statement, all variables and given/known data
    A pen contains a spring with a spring constant of 221 N/m. Whe the tip of the pen is in its retracted position, the spring is compressed 4.90 mm from its unstrained length. In order to push the tip out and lock it into its writing position, the spring must be compressed an additional 5.20 mm. How much work is done by the spring force to ready the pen for writing? Be sure to include the proper algebraic sign with your answer.

    2. Relevant equations
    W elastic=.5kx^2

    3. The attempt at a solution
    I have no idea what they mean by keep an algebraic answer and where does x final come in to the equation along with the additional x value.
  2. jcsd
  3. Dec 3, 2009 #2


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    Science Advisor
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    Gold Member

    this is the Potential Energy of the spring when it is displaced a distance x from its unstretched position. Don't confuse work with Potential Energy.
    The work done by a force moving through a distance can be plus or minus (or 0). They want to know here if the work done by the spring is positive or negative (or 0), and what is its value. That's what they mean by an algebraic answer. What do you know about the relationship between the work done by a spring and its potential energy change?
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