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Homework Help: Spring Question? How much does the block move?

  1. Dec 17, 2008 #1
    A spring with a pointer attached is hanging next to a scale marked in millimeters. Three different packages are hung from the spring. W1 is 110 N, and hangs 40mm from the spring, W2 is 240N and hangs 60mm from the spring W3 is x N and hangs 30 mm from the spring

    What mark on the scale will the pointer indicate when no package is hung from the spring?

    What is the weight W of the 3rd package?

    W = -1/2k(x22-x12)

    One thing I wasn't sure about was this equation--are x1 and x2 in the correct order here because you're looking at the work done to stretch a spring?

    3. I figured out that I had to create a system of equations from the two given weights, 110 N and 240 N, using the equation above. After converting mm to meters, I got two equations--

    14.4 = -0.0018k + 0.5kx12
    4.4 = -0.0008k + 0.5x12

    I solved for k, got -10,000, and plugged back in, and got a length of 26.8 m--is that right? Because my online homework thing tells me I'm wrong....
    Last edited: Dec 17, 2008
  2. jcsd
  3. Dec 17, 2008 #2


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    Homework Helper

    I think you have the wrong equation. The problem is about Forces, not Work.

    Consider using F = -k*x
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