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Energy Problem involving Friction and Spring

  1. Nov 12, 2009 #1
    1. The problem statement, all variables and given/known data

    A wooden block with mass 1.30 kg is placed against a compressed spring at the bottom of a slope inclined at an angle of 35.0 degrees (point A). When the spring is released, it projects the block up the incline. At point B, a distance of 4.15 m up the incline from A, the block is moving up the incline at a speed of 5.00 m/s and is no longer in contact with the spring. The coefficient of kinetic friction between the block and incline is [tex]\mu[/tex]k = 0.450. The mass of the spring is negligible.


    Calculate the amount of potential energy that was initially stored in the spring.
    Take free fall acceleration to be g = 9.80 m/s^2.

    I don't really know what to do.

    I start by doing some energy graphs



    (Initial) Us = KE + [tex]\Delta[/tex]Uint (Final State)

    1/2K[tex]\Delta[/tex]x2 = 1/2mv2+[tex]\mu[/tex]mgcos[tex]\theta[/tex]*L

    L being 4.15m
     
  2. jcsd
  3. Nov 12, 2009 #2

    rl.bhat

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    Homework Helper

    In the energy equation you have not included the potential energy.
     
  4. Nov 12, 2009 #3
    PE is included because the block is at a location higher than it's initial position right?
     
  5. Nov 12, 2009 #4

    rl.bhat

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    What is the final position of the block from the horizontal surface?
    ΔUint includes only the work done against the frictional force.
    So one more term must be there in the energy equation.
     
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