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Homework Help: Conservation of Energy and Springs. Block dropped onto a spring

  1. Feb 26, 2010 #1
    1. The problem statement, all variables and given/known data[/b
    A 2.7 kg block is dropped from rest from a height of 4.5 m above the top of the spring. When the block is momentarily at rest, the spring is compressed by 25.0 cm. What is the speed of the block when the compression of the spring is 15.0 cm?

    2. Relevant equations
    3. The attempt at a solution

    Ok so what I did at first was use PE= U(s) to find the spring constant, which i got to be 4026 N/m (I don't know if this is right, correct me if I'm wrong), after I found that, i used mgh + .5mv^2 = .5kx^2, where h was .1m, and x was .15 since it was compressed .15m. but its wrong. please help!
  2. jcsd
  3. Feb 26, 2010 #2
    1) If the v = 7.52 m/s, I would ask how you found k? I* punched few numbers and had different k (~3000)
    2)Why you are taking h to be 0.1 m? in mgh + .5mv^2 = .5kx^2
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