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Homework Help: Normal Force

  1. Oct 14, 2008 #1
    1. The problem statement, all variables and given/known data
    Three blocks are arranged in a stack on a frictionless horizontal surface. The bottom block has a mass of 37.0 kg. A block of mass 18.0 kg sits on top of it and a 20.0 kg block sits on top of the middle block. A downward vertical force of 170 N is applied to the top block. What is the magnitude of the normal force exerted by the bottom block on the middle block?



    2. Relevant equations
    Fn + T + (-mg) = 0


    3. The attempt at a solution
    20 + 18 = 38*9.8 = 372.4 N
    Fn + 170 - 372.4 = 0
    Fn = 202.4
     
  2. jcsd
  3. Oct 14, 2008 #2

    Doc Al

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    Staff: Mentor

    Good.
    Careful: That 170 N force acts downward.
     
  4. Oct 14, 2008 #3
    So the 170 needs to be negative .. ?
    Fn + (-170) - 372.4 = 0
    Fn = 542.4
     
  5. Oct 14, 2008 #4

    Doc Al

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    Staff: Mentor

    Looks good!
     
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