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Homework Help: Incredibly complicated for basic physics

  1. Sep 22, 2010 #1
    1. The problem statement, all variables and given/known data

    You place a book flat on a table and press down on it with your right hand. The hand-to-book and table-to-book coefficients of kinetic friction are 0.47 and 0.44 respectively. The book's mass is 0.84 kg and your downward push on it is 9.00 N. Now, you use your left hand to push the book along the table at constant speed. Assuming that your right hand is stationary with respect to the table, what is the horizontal force exerted on the book by your left hand?

    2. Relevant equations

    3. The attempt at a solution

    think its got something to do with the fact that the two friction coefficients are like a sandwich on the book. the x direction equation is the force you push the book with minus the two frictions added together= mass times acceleration but I cant get it to work. HELPPPPPPPPPPPPPPP ive spent an hour on this any push in the right direction is appreciated before I lose my damn mind
  2. jcsd
  3. Sep 22, 2010 #2


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    Homework Helper
    Gold Member

    Yes, that much is correct. But don't forget the problem statement says, "use your left hand to push the book along the table at constant speed." What is the acceleration of something moving at a constant velocity?

    You've mentioned that you've worked on this for an hour. So show us your work! :smile: Maybe we can help you once we see what you've done specifically, and where you are stuck.
  4. Sep 22, 2010 #3
  5. Sep 22, 2010 #4
  6. Sep 22, 2010 #5
    You must remember that kinetic friction has a dependence of the Normal Force (N). So if you sum the forces in the x direction you get :

    Fx = Fh - Fk= ma; (Fh = Force by hand; Fx = force of friction) what is acceleration if it is constant????

    Kinetic Friction is =[tex]\mu[/tex]k*N

    You can now plug in your frictional force, and solve for the force due to your hand
    Last edited: Sep 22, 2010
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