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Block-spring Problem

  1. Feb 14, 2008 #1
    1. The problem statement, all variables and given/known data
    A 2- kg block rests against one end of a horizontal spring which is compressed by 18 cm. When the spring is released, the spring forces the block to slide across a table top. It stops 47 cm from where you released it. The spring constant k is equal to 120 N/m. Calculate the constant of kinetic friction μk between the block and the table.


    2. Relevant equations
    W=.5kx^2
    W=Fd


    3. The attempt at a solution
    I used the two equation above to find that F=4.136N

    Somebody suggested I should put this into the equation F=μk*F(n), but I don't know how to find F(n). Any help?
     
  2. jcsd
  3. Feb 14, 2008 #2

    Doc Al

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    Staff: Mentor

    The table is horizontal. Consider the vertical forces acting on the block.
     
  4. Feb 14, 2008 #3
    Okay, gravity? How do I apply that to this problem?
     
  5. Feb 14, 2008 #4

    Doc Al

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    Gravity is one of the forces on the block.

    Answer this: A block sits on the table. What normal force must the table exert on the block?
     
  6. Feb 14, 2008 #5
    Okay I got it -- F(n) is the normal force... the weight of the object. Thanks.
     
  7. Feb 14, 2008 #6

    Doc Al

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    That's it.
     
  8. Feb 14, 2008 #7
    Consider the work done by frictional force. It will be equal to?
    μk x Normal Force = ?
     
  9. Feb 14, 2008 #8

    Doc Al

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    Staff: Mentor

    That's the friction force. How do you find work?
     
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