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What forces should be included?

  1. Sep 28, 2005 #1
    Hi,
    I think that this question need the idea of torque.
    But i m get stuck in choosing which point and what forces should be included.
    Here it is :

    A cylinder with mass m=50kg located as shown in the figure.
    Given that h = 0.5r
    A force F is applied tangentially to the axle to lift the cylinder.
    The minimum value of F is ________
     

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  2. jcsd
  3. Sep 28, 2005 #2
    Hint: as the cylinder moves over the step there is a point that will have complicated normal and frictional forces. That is the point that you most want to leave out of your analysis so that is the point that you to calculate the moments about.
     
  4. Sep 28, 2005 #3

    FredGarvin

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    Science Advisor

    Remember your basic statics equation, [tex]\Sigma M = 0[/tex].

    The toughest part will be to figure out the relation of the contact point B to the center of the cylinder. You will have two forces at work, the weight of the cylinder and the force, F. They will both be acting about B.

    Get your free body diagram going and see what you can reason out from there. You're on the right track with thinging about torque (moments).
     
  5. Sep 28, 2005 #4
    How about the normal force acting on the cylinder?
    Why it is not in consideration?
     
  6. Sep 28, 2005 #5

    Doc Al

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    Staff: Mentor

    Reread gnpatterson's hint. What point will you choose as the pivot for computing torques? Will the normal force exert a torque about that point?
     
  7. Sep 29, 2005 #6
    I mean,the normal force act on the cylinder by the floor.
     
  8. Sep 29, 2005 #7

    Doc Al

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    Staff: Mentor

    When the cylinder loses contact with the floor, that normal force becomes zero.
     
  9. Sep 29, 2005 #8
    Thanks :D

    I got my answer F=283N

    Is that right?
     
  10. Sep 29, 2005 #9

    Doc Al

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    Staff: Mentor

    Looks right to me.
     
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