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Homework Help: Magnitude of normal force question

  1. Oct 6, 2011 #1
    1. The problem statement, all variables and given/known data

    A woman pulls on her suitcase with a force of 105N at an angle of 38 degrees above the horizontal. The coefficients of static and kinetic friction between and suitcase and the floor are 0.273 and 0.117. The mass of the suitcase is 36 kg. what is the magnitude of the normal force acting on the suitcase due to the floor?

    2. Relevant equations

    normal force - weight + vertical component =0

    3. The attempt at a solution

    N - mg +105 sin 38=0

    N=36kg*9.8m/s/s - 105 sin 38 = 288N

    So I have figured out the magnitude of the normal force, but I don't know if the suitcase will slide. How do I figure that out?
    Last edited: Oct 6, 2011
  2. jcsd
  3. Oct 6, 2011 #2


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    Well for the suitcase to move, her horizontal force must be greater than the force of friction. How does friction relate to the normal force and which coefficient of friction would determine if it will move, static or kinetic?
  4. Oct 6, 2011 #3
    Okay, but I'm given two different frictions, but I chose to work with kinetic because I know it's to do with motion... Or at least pretty sure.

    Ff = u(288N)
    Ff = 0.117 x 288N
    Ff = 33.696

    That's so little :S So since she's pushing with 105 N, the suitcase DOES move, correct??
  5. Oct 6, 2011 #4


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    The kinetic friction is used when the body is already moving, in order for motion to occur you'd need to overcome static friction first. But once Fapplied<Ff, then no motion will occur.
  6. Oct 6, 2011 #5
    Thank you makes sense, I got my answer my brother helped & showed me. Although I think you could have been a liiiiittle more like, well :D the formula for calculating Fs is etc, you know? Because you're too smart, & I don't really get it physics language, but now I get what you meant form the starts, thanks ^___^

  7. Oct 6, 2011 #6


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    But you knew what to do! You started correctly by calculating the normal force utilizing the vertical component. I tried to make it simple by how I wrote the second post. (you had all the formulas correct, so I assumed you knew had all the formulas correct)
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