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Homework Help: Hooke's Law Problem

  1. Oct 27, 2013 #1
    A block attached to a spring (which is attached to a wall) lies on a horizontal frictionless surface, and the spring constant is 50 N/m. Initially, the spring is at its relaxed length and the block is stationary at position x = 0. Then an applied force with a constant magnitude of 3.0 N pulls the block in the positive direction of the x axis, stretching the spring until the block stops. When that stopping point is reached, what is the position of the block?

    I tried using Hooke's Law:

    3.0 = 50x

    x = 3.0/50

    x = 0.06 m

    However, when I checked my answer, it said x = 0.12 m.

    Does anyone know what I did wrong? Thank you!
  2. jcsd
  3. Oct 27, 2013 #2

    Doc Al

    User Avatar

    Staff: Mentor

    Hooke's law tells you what force the spring exerts for any given extension. You found the extension that gives a restoring force equal to the applied force. But that just means the net force is zero at that point, not that it stops.

    Hint: Think work and energy, not force.
  4. Oct 27, 2013 #3
    The work done by the force=the potential energy of the block.
  5. Oct 27, 2013 #4
    Thank you for your help!
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