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Spring Force, Distance Problem

  1. Nov 27, 2012 #1
    1. The problem statement, all variables and given/known data
    The spring in the figure has a spring constant of 1400N/m . It is compressed 16.0cm , then launches a 200g block. The horizontal surface is frictionless, but the block's coefficient of kinetic friction on the incline is 0.210.

    FIGURE ATTACHED

    What distance d does the block sail through the air?


    Correct answer: 13.4 m

    2. Relevant equations

    F(spring)=-kx
    F(friction)=μf*FN
    Work=Fdcos(θ)
    Work=(0.5mv22)-(0.5mv12)

    3. The attempt at a solution

    F(spring)=(-1400 N/m)(0.16 m)= 224 N

    F(friction)=(0.210)(cos(45))(0.2)(9.8)= 0.29 N

    224-0.29= 223.71

    Work=223.71d
    Work=(0.5)(0.2)(?)-(0.5)(0.2)(?)


    I think that I should be finding the work and then find distance by dividing by the force. However, I'm not sure how to find the two velocities.
     

    Attached Files:

  2. jcsd
  3. Nov 27, 2012 #2

    tiny-tim

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    Science Advisor
    Homework Helper

    hi rocapp! :smile:
    you can't find d from work or energy, you'll need the usual projectile equations

    to find the initial speed (just before d), use the work-energy method that you have been using (with the block starting with zero speed), but use gravity also :wink:
     
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