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Kinematics Question. Incline, Spring, Friction

  1. Oct 27, 2014 #1
    1. The problem statement, all variables and given/known data
    Practice problem for midterm.
    mKq3pH6.png

    2. Relevant equations

    T_1+U_1=T_2+U_2
    U_spring=1/2kx^2


    3. The attempt at a solution

    Set X-axis along the 30 degree line and the Y-axis perpendicular.

    I'm not sure how to consider the friction constant into the formula.

    Any help is very much appreciated.
     
  2. jcsd
  3. Oct 27, 2014 #2

    Simon Bridge

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    hint: work against friction.
     
  4. Oct 27, 2014 #3

    gneill

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    Staff: Mentor

    Calculate the friction forces (static and kinetic). Make sure the block can move when released (static friction). If the block moves against friction (kinetic friction), what work is done? What happens to the energy involved in friction?
     
  5. Oct 28, 2014 #4
    sumF_y=0
    N-mgcos30=0
    N=17 N

    sumF_x=0
    F_spring-F_friction=m_block*accel_block
    kx-uN=ma

    if static, accel=0

    410(0.5)-u(17)=0
    u=12.06

    doesnt seem right... i think the x is wrong for the spring but i can't visualize it.
     
  6. Oct 28, 2014 #5

    gneill

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    Staff: Mentor

    You want to compare the spring force with the static friction force. What must the relationship be if the block is to be able to move from rest?
     
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