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Homework Help: Draw free body diagrams for each sphere

  1. Jul 7, 2005 #1

    Determine the reaction forces at the four contact points A,B,C,D. The hollow balls which are homogenous and made of the same material have masses of 1.02kg and 2.04kg and the chamber they sit in is 55.98cm wide. Everything is smooth,so that the friction is negligible.

    Can anyone help me in this question?

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  3. Jul 7, 2005 #2


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    Draw free body diagrams for each sphere. In the absence of frictional forces, there are only normal forces to consider: right at A, left at C, and up at D. The forces at B point along the line connecting the centers of the spheres. Each sphere has weight acting downwards. The hard part is finding the angle between line connecting sphere centers and the horizontal (or vertical). You need to know the size of the spheres. Do you have these? From the two FBDs you will get four equations for the four unkowns. These will easily reduce to two equations because two of the four force magnitudes must be the same, and one must equal the total weight.
  4. Jul 7, 2005 #3
    opps...I forgot to mention the radius of circles...10 cm and 20cm for each.
  5. Jul 7, 2005 #4
    since I got the value of radius,I can find out the angle of tbetween the line connect both center and the horizontal/vertical
    But...find it for what?
  6. Jul 7, 2005 #5


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    With this angle you can resolve the action-reation pair of forces acting at B into horizontal and vertical components. All the other forces in the problem are either horizontal or vertical. The vector sum of the forces on each sphere must be zero, and that leads to two equations for each sphere (one for horizontal forces and one for vertical forces). That will give you all the equations you need to solve for all four unknown forces.
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