Rotational kinetic energy and moment of inertia

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Homework Help Overview

The discussion revolves around the calculation of rotational kinetic energy and the moment of inertia for a rotating object, specifically a CD with given mass and radius. The original poster attempts to apply the kinetic energy formula for rotational motion.

Discussion Character

  • Conceptual clarification, Mathematical reasoning

Approaches and Questions Raised

  • Participants discuss the appropriate formula for the moment of inertia, with an initial incorrect assumption about its value for a disk. There is an exploration of the correct expression for the moment of inertia.

Discussion Status

The conversation has progressed with participants clarifying the correct formula for the moment of inertia of a disk. Some guidance has been provided regarding the necessary adjustments to the original poster's approach.

Contextual Notes

There is a focus on ensuring the correct application of formulas related to rotational motion, with specific attention to the definitions and assumptions regarding the moment of inertia.

court2011
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Homework Statement



A 16 g CD with a radius of 6.0 cm rotates with an angular speed of 42 rad/s.
(a) What is its kinetic energy?

Homework Equations



k=1/2Iw^2

The Attempt at a Solution


k=1/2(0.016x0.0036)(1764)=0.05 J
 
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Careful. The moment of inertia of a disk is not MR^2. That's the moment of inertia for a hoop, or for a point mass.
 
ohhh so should i have 1/2mr^2
 
Yup.
 
kk sweet thanks! i got it right :)
 

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