Kinetic Energy of Rolling Motion

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Homework Help Overview

The problem involves calculating the kinetic energy of a rotating object, specifically a CD, using its mass, radius, and angular speed. The subject area is rotational dynamics and energy calculations.

Discussion Character

  • Exploratory, Mathematical reasoning, Assumption checking

Approaches and Questions Raised

  • Participants discuss the appropriate formula for calculating rotational kinetic energy and question the correctness of the original poster's calculations. There is an exploration of unit consistency and the application of the formula.

Discussion Status

The discussion includes attempts to clarify the formula for rotational kinetic energy and checks for potential errors in calculations. Some participants provide guidance on ensuring proper unit tracking, while others reflect on their own mistakes in applying the formula.

Contextual Notes

There is a mention of a specific numerical error related to the factor of 1/2 in the kinetic energy formula, indicating that participants are actively engaging with the mathematical details of the problem.

Cici2006
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Homework Statement


A 12g CD with a radius of 7.0 cm rotates with an angular speed of 35 rad/s.
What is its kinetic energy?


Homework Equations





The Attempt at a Solution


I used K=(1/2)mv^2(1+I/mr^2)
v=[tex]\omega[/tex]r=(35rad/s)(0.07m)=2.45m/s
K=(1/2)(0.012kg)(2.45m/s)^2(1)=0.36

And it's wrong. Am i using the right formula? What should I do
 
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For rotational KE, use:
[tex]{KE} = 1/2 I \omega^2[/tex]
 
I used that too and i still got it wrong.
 
Are you keeping track of units. If its not the problem, just show your calculation
 
Oh I know what i did wrong now i forgot to multiply by 1/2. THanks for the help
 

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