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Homework Help: Force questions need help

  1. Jan 30, 2010 #1
    1. The problem statement, all variables and given/known data

    A force of 10 newtons toward the right is exerted on a wooden crate initially moving to the right on a horizontal wooden floor. the crate weights 25 newtons.

    A) calculate the magnitude of the force of friction between the crate and the floor

    B) name the vertical forces acting on the crate

    C) name the horizontal forces acting on the crate

    D) what is the magnitude of the net force acting on the crate

    E) is the crate accelerating?

    2. Relevant equations

    A) u*Fn = ff (how can i find out u?)

    b) weight is 25 newtons so fg and fnormal is 25 newtons

    c) applied force is 10 newtons

    d) m*a = f net or applied force - ff = fn (mass and acceleration isnt given so i cant use it)

    3. The attempt at a solution

    im stuck with the equations can someone help =)
  2. jcsd
  3. Jan 30, 2010 #2


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    Moving crate on the wooden floor will come to rest due to frictional force. If you want to keep it moving, you have to apply a force to overcome the frictional force. If the crate moves with uniform velocity, then the frictional force is equal to the applied force.
  4. Jan 31, 2010 #3
    emm there is an apply force on the crate but how i know if it moves in uniform velocity?
  5. Jan 31, 2010 #4
    can someone help me figure out the force of friction?
  6. Jan 31, 2010 #5


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    As rl.bhat noted, the friction force must equal the applied force if the crate is moving with constant velocity. The problem statement, however, is incomplete. Is there missing information? Without knowing that it moves with constant velocity, it cannot be solved without additional data.
  7. Jan 31, 2010 #6
    what is missing?
  8. Feb 1, 2010 #7


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    you don't, unless the problem tells you that
  9. Feb 1, 2010 #8
    hmm so can this problem be solved?
  10. Feb 1, 2010 #9


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    It can be solved only if you assume that the crate moves at constant velocity under the application of the 10 N applied force.
  11. Feb 1, 2010 #10
    so if it moves at constant velocity what can i do to solve the frictional force is there a equation?
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