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Homework Help: Book sandwiched between your hand and table

  1. Jun 6, 2015 #1
    Hi, I have been working on this problem for a while:

    1. 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 0.48 and 0.43 respectively. The book's mass is 1.14 kg and your downward push on it is 9.70 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?
    I think I have the right idea, which is because the speed is constant, there is no acceleration. So the force should be equal to the 2 frictions. But I keep getting the answer wrong. I'm basically stuck because I can't find where I'm making the mistake.

    Fx = .48 (9.7) + .43( 1.14 x 9.8) = 9.46 N

    Am I calculating the normal forces wrong? I just assumed by N3L that 9.7 is the normal for the hand pushing down and the weight = the normal for the book on the table.

    Your help will be much appreciated!
  2. jcsd
  3. Jun 6, 2015 #2
    Your hand pushing down on the book will increase the normal force at both interfaces, so at the book/table interface the normal force will be caused by your hand pushing down as well as the book's weight.
  4. Jun 6, 2015 #3
    Okay, so my equation should be Fx = .48 (9.7) + .43( 11.72 + 9.7)?
  5. Jun 6, 2015 #4
    Got it! Thanks! : )
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