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Homework Help: Work Energy Method for Linear Motion

  1. Jul 3, 2012 #1
    1. The problem statement, all variables and given/known data
    From my textbook there is a note that says " A reference datum must always be define in order to obtain the height h. I don't quite understand what is it trying to tell me.

    I already had define my datum 1 as position 1 and datum 2 as position 2.
    On my 2nd diagram , I made a red line, is that the Height that I need to find?
    3. The attempt at a solution
    Working for Block position 2
    =1/2(10)v^2 + 10(9.81)(-h) + 0


    Attached Files:

    Last edited: Jul 3, 2012
  2. jcsd
  3. Jul 3, 2012 #2
    I gave a try to your problem and got the answer to be 2.74 which is almost near to 2.94, that might be because i used g=10m/s^2 for simplified calculation.

    The spring is compressed and released, the spring potential energy converts to kinetic energy, gravitational potential energy and some gets used up in doing work again friction. Can you make the equation now?
  4. Jul 3, 2012 #3
    Ignore the 1st diagram.

    Attached Files:

    • a2a.jpg
      File size:
      36.2 KB
  5. Jul 3, 2012 #4
    Hi Pranav, you are asking me to make an equation for datum 1 or datum 2?
  6. Jul 3, 2012 #5
    Sorry Pranav, it's getting late here, talk to you tomorrow.
  7. Jul 3, 2012 #6
    Ah that makes more sense, i was confused what you meant by "datum".

    I am asking you to use the conservation of energy at datum 1 and datum 2. Also shift datum 1 a little back because the spring is compressed by 80mm, it will make things easier for you.
    Define zero gravitational potential energy at datum 1, now what is the spring potential energy?
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