What is the correct moment of inertia for part a using I=m*r^2?

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Homework Help Overview

The discussion revolves around calculating the moment of inertia for a uniform disk and its application in kinetic energy equations. Participants are exploring the correct formula and units needed for their calculations.

Discussion Character

  • Exploratory, Assumption checking, Conceptual clarification

Approaches and Questions Raised

  • Some participants attempt to calculate the moment of inertia using the formula I=m*r^2, while others use I=1/2MR^2. There are questions regarding the correct units for angular velocity (ω) needed in the kinetic energy formula.

Discussion Status

Participants are actively sharing their calculations and questioning the correctness of their results. There is a recognition of the need to clarify the units for angular velocity, with some guidance provided on converting from revolutions per second to radians per second.

Contextual Notes

There appears to be confusion regarding the appropriate formula for moment of inertia and the necessary units for angular velocity in the kinetic energy equation. Participants are working within the constraints of the problem but have not reached a consensus on the correct approach.

Sneakatone
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for part a I used the equation I=m*r^2 ---> 120(58/100)^2=40.36 kg*m^2

b)I know how to do this using the equation K=1/2Iw^2 but my moment of inertia is incorrect.
 

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Sneakatone said:
for part a I used the equation I=m*r^2 ---> 120(58/100)^2=40.36 kg*m^2

b)I know how to do this using the equation K=1/2Iw^2 but my moment of inertia is incorrect.
What is the moment of inertia of a uniform disk of mass, M, and radius, R ?
 
I used the equation 1/2MR^2 and got =20.18.
when I plugged everything into the KE equation I had 305.22 J but that is incorrect.
 
Sneakatone said:
I used the equation 1/2MR^2 and got =20.18.
when I plugged everything into the KE equation I had 305.22 J but that is incorrect.

What are the units for ω ?
 
rev/s
 
Sneakatone said:
rev/s

The rotation rate is given you in rev/s, but what units does it need to be into plug it into the formula for KE?
 
should it be rev/min or rad/s?
 
I got it now it should be in rad/s for some reason I thought It was suppose to be rev/s.
Thank you all!
 

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