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Homework Help: What is the force the pole exerts on the ball?

  1. Oct 8, 2006 #1
    A tether ball leans against the post to which it is attached. The string is attached to the ball such that a line along the string passes through the center of the ball. The string to which the ball is attached has length 1.50 m and the ball's radius is 0.105 m and has a mass of 0.266 kg . Neglect any friction between the ball and the pole.

    What is the force the pole exerts on the ball?

    I found the Tension in the rope to be 2.61 N, and mulitpling that times the sin of the angle i got .183 N the answer is incorrect.

    A small box of mass m1 is sitting on a board of mass m2 and length L. The board rests on a frictionless horizontal surface. The coefficient of static friction between the board and the box is U_s. The coefficient of kinetic friction between the board and the box is, as usual, less than U_s.

    Throughout the problem, use g for the magnitude of the acceleration due to gravity. In the hints, use Ft for the magnitude of the friction force between the board and the box.

    Find F(minimum) , the constant force with the least magnitude that must be applied to the board in order to pull the board out from under the the box (which will then fall off of the opposite end of the board).

    I cant find any example of this one in my book, i must be missing forces. I tried doing each of the masses seperately in relation to what they are on top of, but im not getting it.

    Thank you in advance for any help :)
  2. jcsd
  3. Oct 8, 2006 #2
    How did you go about trying to solve these problems?

    For your first one, the thing to do will be to draw a free body diagram and account for all the forces, and angles too (though I don't see any in your original write up). If you put up some work then maybe some one can find where you went wrong.

    For this next problem you are trying to solve for when the sum of the forces is greater than static friction, such that the box on top slips away. Again, it's hard to know where you are having difficulties without seeing the approach you take.
  4. Oct 8, 2006 #3
    nevermind on the first one, i wasn't taking into consideration the length of the rope plus the ball for the denominator.

    Can anyone point me in the right direction for the second one?
  5. Oct 9, 2006 #4


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    Staff: Mentor

    Show us explicitly what you've tried so far. Then someone can probably point out where your problem is. It's much more efficient than for us to shoot blindly in the dark and hope we hit upon your problem! :smile:
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