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Energy and hook's law

  1. Sep 29, 2014 #1
    1. The problem statement, all variables and given/known data
    A 205 g cube slides down a ramp starting from rest as shown in the figure below. The ramp has a 46° slope. After falling a distance of 92 cm, the cube strikes a spring of spring constant
    k = 21 N/m.
    Find the maximum compression of the spring when the coefficient of kinetic friction between the cube and the ramp is 0.13.
    http://puu.sh/bTjhN/ed172bac4f.png [Broken]

    2. Relevant equations

    conservation of energy laws
    f=ma

    3. The attempt at a solution
    I solved for work of friction, the work of gravity and the work of spring (d is vertical distance of 92cm and x is the distance of compression)

    http://puu.sh/bTjoU/221afafc3f.png [Broken]

    I then used the conservation of energy law to piece together my 3 equations
    http://puu.sh/bTjw6/e9c0236b16.png [Broken]

    apparently my equation didn't match with the answer's. Can someone please tell me why?? and what did I miss??
     
    Last edited by a moderator: May 7, 2017
  2. jcsd
  3. Sep 29, 2014 #2

    Simon Bridge

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    Looks OK to me - what was the model answer?
     
  4. Sep 30, 2014 #3

    rude man

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    Looks right to me also.
     
  5. Sep 30, 2014 #4
    http://puu.sh/bTRBF/53f9460841.jpg [Broken]
    This is the textbook answer, could it be that the textbook is misprinted???
     

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    Last edited by a moderator: May 7, 2017
  6. Sep 30, 2014 #5

    rude man

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    Probably a typo.
    Either put a slash between μ and tan(θ) or change tan(θ) to cot(θ).
     
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