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Spring and height of block

  1. Feb 26, 2015 #1

    Suraj M

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    Gold Member

    1. The problem statement, all variables and given/known data
    A block of mass 250 g is kept on a vertical spring with spring constant 100N/m fixed from below.
    The spring is now compressed to have a length 10 cm shorter than its natural length and is released. How high does the block rise?g = 10m/s
    2. Relevant equations
    and other basic equations

    3. The attempt at a solution
    So I found out initial energy imparted,
    $$E_1 = ½kx² = 0.5 J$$
    then equated to change in potential and new spring energy.
    $$E_2 = mgh + ½k(x-h)²$$ where h is the height required
    solving E₁= E₂, I get an awkward answer. the answer given is 20 cm. How?
  2. jcsd
  3. Feb 26, 2015 #2
    Your E2 is incorrect .

    Why do you think spring would have elastic potential energy when the block leaves it ?
  4. Feb 26, 2015 #3

    Suraj M

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    Gold Member

    Oh so you're assuming the block is not attached to the spring, huh, didn't consider that!
    Oh i get the right answer then, its just a regular launch. thank you Tanya!
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