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What is the initial potential energy in the spring?

  1. Oct 9, 2007 #1
    1. The problem statement, all variables and given/known data
    A wooden block with mass 1.75 kg is placed against a compressed spring at the bottom of a slope inclined at an angle of 34.0 (point ). When the spring is released, it projects the block up the incline. At point , a distance of 4.55m up the incline from , the block is moving up the incline at a speed of 5.85 m/s and is no longer in contact with the spring. The coefficient of kinetic friction between the block and incline is = 0.55. The mass of the spring is negligible.

    What is the initial potential energy in the spring??

    2. Relevant equations
    ok, I know that you do kinetic energy + potential energy +friction
    K = .5mv^2
    U = mgh
    U of spring = .5*k*v^2


    3. The attempt at a solution

    But How do i account for the angles and mu, if some one could show me the equation..I would understand. I have tried everything.. Thanks in advance
     
  2. jcsd
  3. Oct 9, 2007 #2

    PhanthomJay

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    The angle will help you to determine 'h' in the 'mgh' term, and also will aid in determining the value of the normal force used in your calcuation of the friction force.
     
  4. Oct 9, 2007 #3
    how would i calculate h though? i don't know?? please help
     
  5. Oct 9, 2007 #4
    would h just be mgmucostheta
     
  6. Oct 9, 2007 #5

    PhanthomJay

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    No, what's h got to do with mu?
    h is the height that the block reaches above ground when it is 4.55m up the incline. From trig, h is just 4.55 sin theta, no?
     
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