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Consider the following situation:

Two balls are inside a jar with diameter $D$. The balls are uniform in mass and both have the same diameter $d$.

enter image description here

Express the forces that acts at the colored dots in the figure.

Could any body give me a hint? It seems to me that I can't express one force without using the other.

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closed as off-topic by John Rennie, Danu, Chris White, Kyle Kanos, Bernhard Aug 29 at 13:23

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You know there is a force $mg$ acting downwards at the centre of each ball. You known the balls aren't rotating so the moments of the forces add up to zero, and the balls aren't accelerating so you know the forces on each ball must add up to $mg$ upwards. So you can down a series of simultaneous equations relating the forces. –  John Rennie Aug 29 at 10:43
    
I solved the question. Thanks to both of you. –  Udi Behar Aug 29 at 11:27

1 Answer 1

Consider this for the upper ball:

enter image description here

The angle of the inclined plane is simply derived from geometrical considerations. Looks pretty easy to solve, right? Once you know the normal force of the inclined slope, reflect and apply it to the bottom ball to complete the problem.

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Nice post, I made you cross 2k –  bobie Aug 29 at 12:12
    
Very good approach. The right diagram makes all the difference. –  Floris Aug 29 at 12:13

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