Wednesday, August 17, 2011

Find the moment of inertia of a ring about an axis through the center and normal to the plane of the ring and estimate its error.The flat circular...

We'll apply the formula of the moment of
inertia:


I = (pi*sigma/2)(a^4 -
b^4)


Knowing, from enunciation, the mass of the circular
ring is:


 I = (M/2)(a^2 +
b^2)


We'll insert the given
values:


I = 0.191(0.110^2 +
0.015^2)/2


I = 1.177*10^-3
Kg*m^2


The absolute error in a is delta
a.


The fractional error in a is delta
a/a.


The fractional error in a^2 is 2delta
a/a.


The absolute error in a^2 is 2adelta a and the
absolute error in ab2 is 2bdelta b.


The absolute error in
a^2+b^2:


a^2+b^2 = sqrt[4a^2(delta a)^2 + 4b^2(delta
b)^2]


a^2+b^2 = 1.23*10^-2
m^2


From this value results a fractional
error of 1.8%.


The fractional error in M is
:


M = (0.003/0.191)


M =
1.6%


I = sqrt(1.8^2 + 1.6^2)
%


I =
2.4%


I = 1.177*10^-3 Kg*m^2 
+/- 2.4%

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