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Homework Help: Conservation of Energy Problem

  1. Dec 12, 2013 #1
    1. The problem statement, all variables and given/known data

    Using the Principle of Conservation of Energy, solve:

    A block of mass 5kg is released from rest and slides down a distance D
    down a smooth plane inclined at 30◦ to the horizontal. It then strikes a
    spring compressing it 10cm before it begins to move up the plane. If the
    spring constant is 980N/m and g = 9.8m/s2, find D.

    2. Relevant equations



    3. The attempt at a solution

    Using mgh=0.5(k)(x^2)


    and got h on its own for:


    Then I used d=hcos(theta) to get:

    d= (.001)cos(30)

    d= 8.66×10^-4

    Is this the correct way of doing the question? Thanks for any advice.
  2. jcsd
  3. Dec 12, 2013 #2


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    Your trig is wrong. D is the hypotenuse of the triangle, and h is the side opposite the angle. Draw a picture.
  4. Dec 12, 2013 #3
    Hi cepheid thanks for the quick reply.

    I see so d=h/sin30 then is it?
  5. Dec 12, 2013 #4


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    That is correct. The rest of your work (applying the conservation of energy( looks fine.
  6. Dec 12, 2013 #5
    Brilliant! Thanks a million for the help!
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