geerky42
  • geerky42
Help Needed with Inertia...
Physics
  • Stacey Warren - Expert brainly.com
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katieb
  • katieb
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geerky42
  • geerky42
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anonymous
  • anonymous
ah... so the first thing you need to do is calculate the location of the centre of mass.. can you do that?
geerky42
  • geerky42
Yeah, it's 1.95 m away from 1kg mass.

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geerky42
  • geerky42
Not sure what to do in next step...
anonymous
  • anonymous
ok.. i won't check that then.. fine.. now answer this.. if i know that there is a mass that is connected to a string.. which has a length 'l'.. and i swirled it.. what would be the moment of inertia???
anonymous
  • anonymous
|dw:1359715230549:dw|
geerky42
  • geerky42
\(\large I = \dfrac{1}{3}ml^2\), right?
anonymous
  • anonymous
noooOOO :O.. how did you get that? :O
anonymous
  • anonymous
its a point mass.. imagine its a point mass!!
geerky42
  • geerky42
Idk, it's a formula for end of rod, though this is what you asked for, sorry
anonymous
  • anonymous
no.. what is the general formula for moment of inertia?? i think the concept itself is not clear to you.. huh?
geerky42
  • geerky42
You mean \(\large I = ml^2\)?
geerky42
  • geerky42
it's a general formula for inertia, i think.
anonymous
  • anonymous
its \[\sum_{ }^{ } mR ^{2}\]
anonymous
  • anonymous
thats the general formula.. and in my question .. since only one point mass is present.. you can say its just \[ml ^{2} \]
geerky42
  • geerky42
So for my question, I just use the sum of inertia?
anonymous
  • anonymous
so its basically summasation of all point mass times their distance from the axis of rotation squared.. so in your question.. you have 2 point masses.. so find each one's moment of inertia and sum it up
anonymous
  • anonymous
and don't call it inertia.. its called moment of inertia :P
anonymous
  • anonymous
inertia = resistance to change for linear motion moment of inertia = resistance to change for rotational motion
geerky42
  • geerky42
ok I see. does this formula \(\displaystyle\int r^2 \text{d}m\) work too? I tired this way and I got lost.
anonymous
  • anonymous
that is only if you have a rigid object.(continuos distribution of mass). but in your case its not a rigit object... its just 2 point masses.. !! so you can indivisually find their moment's of inertia about the rotational axis and sum them up..
geerky42
  • geerky42
I see. Thanks!
anonymous
  • anonymous
your welcome :)

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