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Homework Help: Coefficient of Friction of a wooden box

  1. Dec 3, 2006 #1
    1. If a wooden box was pulled up the inclined plane at a constant speed using a spring scale. How would an equation be derived for uk, us, Ff, and N.

    2. Relevant equations
    So to get N. The equation would be N=mg-F (sin (theta)).
    with F being the reading on the spring scale.
    Ff would be the opposite of the pulling force F, from what is read in the spring scale.
    So when pulling upward (tan (thetha)) is not used to find uk or us.
    So I need help because I dont know wat the equation would be for Uk or Us. And if I am deriving N or Ff the right way.

    3. The attempt at a solution
  2. jcsd
  3. Dec 3, 2006 #2


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    Homework Helper

    It appears that the only thing you need now is the relation between the force of friction Ff and uk (or us).
  4. Dec 3, 2006 #3
    Is this right?

    If F=ukN
    with F being the reading on the spring scale when the box is being pulled at constant speed

    with F being the reading on the spring scale when the box starts to move.
  5. Dec 4, 2006 #4


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    Since you stated that the force makes an angle other than zero with the incline, then the force of friction (static/kinetic) equals F*cos(theta), where theta is the angle between the force and the incline, and F is the reading on the scale. Plug thta into the equations above, combine with the expression you got for N, and you should get your relation.
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