What is the Center of Mass for a Donut and an Empty Box within a Box?

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The discussion focuses on determining the center of mass (CoM) for a donut shape and an empty box within a box. Participants are encouraged to share their attempts at solving the problem and clarify their understanding of the CoM, particularly in relation to symmetry. There is a mention of whether the figures are 3D, specifically questioning if the donut is a torus. The conversation also hints at the importance of symmetry in finding the CoM. Overall, the thread seeks collaborative problem-solving for understanding the CoM in these specific shapes.
immeen04
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1. FIgures in this link:
( a donut, and a Box with and empty box inside)
http://postimage.org/image/smdut3cxb/ 2.Find the CoM of the two figures
3. as i attempted for the circle:

Homework Statement


Homework Equations


The Attempt at a Solution

 
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Welcome to PF;
How have you attempted these problems?

Do you understand where the com would be if the hole weren't there?
Are these images 3D? i.e. is the circular one literally a torus (a donut shape)?
 
One word hint...Symmetry
 
erm :redface: … guys …

haven't you notived the edit about two hours ago? :wink:​
 
Anyone know how to solve problems involving glases/lenses :-)
 
Nah - nobody reads those messages :)
 
Thread 'Correct statement about size of wire to produce larger extension'

Thread 'Correct statement about size of wire to produce larger extension'

The answer is (B) but I don't really understand why. Based on formula of Young Modulus: $$x=\frac{FL}{AE}$$ The second wire made of the same material so it means they have same Young Modulus. Larger extension means larger value of ##x## so to get larger value of ##x## we can increase ##F## and ##L## and decrease ##A## I am not sure whether there is change in ##F## for first and second wire so I will just assume ##F## does not change. It leaves (B) and (C) as possible options so why is (C)...
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