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Homework Help: Forces Test Redo

  1. Mar 2, 2008 #1
    Our professor is letting us redo the questions we missed on our exam for half-credit because the averages for his classes were 50, 60, and 70. I have a couple of q's I am needing help with, please.

    What is the acceleration of a 1.8 kg physics book sliding down a 36 degree incline if the coefficient of kinetic friction, uk = 0.452?

    What I have so far is Fnetx = Fg sin x (theta) - Ffk. But since Ffk is = uk x Fn, how do I find Fn? Would it be equal to Fg x cos (theta)?

    Am I headed in the right direction at all?
     
  2. jcsd
  3. Mar 2, 2008 #2

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    Right. You are almost there.
     
  4. Mar 2, 2008 #3
    Okay... so I got Fnetx = 3.92 N. would Fnety = 0? How would I find acceleration from that? Completely lost after this. Thanks much.
     
  5. Mar 2, 2008 #4

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    I don't know how you could be, after writing down the correct eqn...

    If total F is along the plane downward, then
    F = component of gravity along plane - frictional force
    = mgsin(theta) - uk*mgcos(theta).
     
  6. Mar 2, 2008 #5
    That is how i got the 3.92 N. So that is all?
     
  7. Mar 2, 2008 #6

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    Why, would you have liked it to be very difficult?

    The mass will cancel out, so write the eqn in symbols like I have done. That'll make it even easier and neater.

    Cheers.
     
  8. Mar 2, 2008 #7
    I just knew there had to be something else to finding the acceleration is all. Thanks much for the help.
     
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