Moment Of inertia - 2

Take a square of side \ell, and remove the "middle'' square (1/9 of the area). Then remove the "middle'' square from each of the remaining eight squares, and so on, forever. Let the final object have mass m. Find the moment of inertia of the final object about the axis through the center of the original square and perpendicular to the plane of the square.

20 Answers

21
tapanmast Vora ·

is it 1/36(mL2)

33
Abhishek Priyam ·

At first i alos took that...and mass also so and i got..

I=7mL2/(64*45) [5]

21
tapanmast Vora ·

OH!!!!!!!!

here L will b the legth of smaller square [5]

I took length of the whole SQ. all da time

33
Abhishek Priyam ·

Ib=72Is
8Is+4m(√2L)2+4mL2=Ib
8Is+12mL2=72Is...

13
deepanshu001 agarwal ·

@priyam post ur eqn plzzz...

21
tapanmast Vora ·

Priyam I guess I m making sum mist. in taking L sumwer, can u pl. post ur steps.

Omit the explanation, jus da steps shall do coz I jus gotta spot da not

11
Anirudh Narayanan ·

Can anyone tell me how close this question comes to jee level of toughness??

33
Abhishek Priyam ·

deepanshu...

kaymant sir confirmed...
3mL2/16

13
deepanshu001 agarwal ·

ml^2/54

33
Abhishek Priyam ·

tapan u got 1/36

i got 3/16 Let us see... what kayamant sir had to say

62
Lokesh Verma ·

Lot of fractals :) ;)

33
Abhishek Priyam ·

.....
64Is=12mL2
Is=3mL2/16

was first doing ... 64/12=4 :D

33
Abhishek Priyam ·

Sorry...

found the msitake...

just a sec... I am calculating that...

66
kaymant ·

No.

33
Abhishek Priyam ·

Got ml2/15

??

66
kaymant ·

Well try to find it out.. really the same idea..only in two dimensions.
By the way, Nishant sir spoke about fractals, and I cannot stop myself from posting a few pics. As sir already said, these are objects which keep on showing the same pattern over and over again no matter how small section you take of that object. In the following three pictures, I have subsequently zoomed into the squared region and see the similarity.

33
Abhishek Priyam ·

Now that the idea is out in the open, try the next one which I have posted.--kaymant Sir..

But i am not able to see the same method here at the first sight...... :(

:(

:(

62
Lokesh Verma ·

http://images.google.co.in/images?q=fractals

62
Lokesh Verma ·

no it is an interesting thing in mathematics

where patterns keep repeating...

Like in snails or in images that you must have seen..
in a lot of leaves..

It is one very very interesting thing.
I am writing an article on it for the magazine.. and somehow kaymant sir got these here :)

in 2 different posts...

11
Subash ·

what is fractals bhaiyya ? a term of higher physics??

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