Moment of Inertia: Mass, Radius, Formula

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SUMMARY

The discussion centers on calculating the moment of inertia for a solid disk with a diameter of 0.51 m and a mass of 5.0 kg. The correct formula for a solid disk is I = (1/2)mr^2, where the radius is 0.255 m. The initial confusion arose from the incorrect application of the formula I = mr^2, which is applicable to cylindrical shells. Ultimately, the participant successfully calculated the moment of inertia after clarifying the correct formula.

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  • Understanding of basic physics concepts, specifically rotational dynamics.
  • Familiarity with the formula for moment of inertia.
  • Knowledge of solid geometry, particularly the properties of disks.
  • Ability to perform calculations involving mass and radius.
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  • Learn about the derivation of the moment of inertia for a solid disk.
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Students studying physics, particularly those learning about rotational dynamics and moment of inertia calculations.

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1. Determine the moment-of-inertia in kg/m^2 of a solid disk 0.51 m in diameter, having a mass of 5.0 kg.



2. I=mr^2



3. I thought the formula was I = mr^2. Mass = 5kg and the radius = .255m, but when I enter the answer of .325 it is incorrect. Am I using the correct formula? Thanks.
 
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No. mr^2 is correct for a cylindrical shell. Your disk is solid. Why don't you look up the correct formula?
 
You know what DICK? I am studying physics for the 1st time and I am working very hard at it so I would appreciate a little courtesy for those of us who "aren't as smart as you"
 
Apologies for being direct, but look. If you think you might have the wrong formula, you might try to look up the formula for the MOMENT OF INERTIA OF A DISK. Is that too much to ask? Geez. Aren't you being a little quick to take offense? Do you expect me to just tell you the answer? Then you are asking too much.
 
I apologize for jumping to offense. I just get frustrated with all of this and it takes me a while to understand some of the problems.

Thanks for helping out.
 
That's ok. I understand people get stressed with unfamiliar material and sometimes I see the answer as far more obvious than they do. You did get it right?
 
Yes, I got it. Thanks again.
 

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