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Homework Help: Finding the distance a spring compresses

  1. Nov 10, 2008 #1
    1. The problem statement, all variables and given/known data

    An object of mass m=2.2 kg is travelling on a horizontal surface. The coefficient of kinetic friction between the object and the surface is µk=0.2. The object has speed v=0.57 m/s when it reaches x=0 and encounters a spring. The object compresses the spring a distance d/2, stops instantaneously, and then travels back to x=0 where it stops completely. What is the total distance, d, that the object moves after first touching the spring?

    2. Relevant equations

    KE+Espring = KEi+Wfriction

    3. The attempt at a solution

    I am really confused I don't think I have enough knowns to solve the problem.
  2. jcsd
  3. Nov 10, 2008 #2


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    I think you may have more information than you realize.

    You start with an initial KE at x = 0.

    There are two sources of work against the mass from that point.

    There is friction and the spring.

    But the spring gains potential energy ... but then gives it back until the object it at rest just as it gets to x = 0 again. So how much net work did the spring do?
  4. Nov 10, 2008 #3
    0 I guess, I don't understand how that helps
  5. Nov 11, 2008 #4


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    If the spring does no net work in stopping the object doesn't all of the kinetic energy of the object need to be accounted for by just the friction over the distance of 2*(d/2) ?

    Doesn't mv2/2 = Work of Friction = Ffriction * distance
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