Calculating Kinetic Energy and Speed with Rolling Hoop Problem

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Homework Help Overview

The problem involves a hoop rolling up a hill and requires calculating the percentage of its initial total kinetic energy that is due to rotational kinetic energy, as well as determining its speed at the top of the hill. The subject area is primarily focused on kinetic energy and rotational motion.

Discussion Character

  • Exploratory, Conceptual clarification, Mathematical reasoning

Approaches and Questions Raised

  • Participants discuss the need for mass and radius in the equations, with one suggesting to use arbitrary values for these variables. There is confusion regarding the answers provided in a study guide, prompting questions about the derivation of those results.

Discussion Status

Some guidance has been offered regarding the relationship between translational and rotational kinetic energy, and how to express these in common terms. Multiple interpretations of the problem are being explored, particularly concerning the use of arbitrary values for mass and radius.

Contextual Notes

Participants express uncertainty about the necessity of specific values for mass and radius, indicating a potential constraint in the problem setup. There is also mention of multitasking and its impact on problem-solving in physics.

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Homework Statement



A hoop, rolling at a constant velocity of 4m/s, rolls up a hill .8 m tall on to flat surface .
a) what percent of its initial total K.E. ( before rolling up the
hill) is due to rotational K.E.
b) how fast is it moving on top of hill.

Homework Equations


i=mr2
w=vr


The Attempt at a Solution


i am completely stumped, every equation i can find either requires a mass or a R or both. This problem looks like it should be easy that's why i feel so dumb for not knowing it.
 
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Just call the mass 'm' and the radius 'R'. You don't need actual values to answer the questions.
 
well my study guide gave me the answers a)50 % b) 2.86. and i don't understand at all how they got that.
 
The plot deepens from that of the last problem--(man you guys are trying to bite off a lot at one time this w/e):

KE(total)=KE(translational)+KE(rotational)

KE(rotational)=1/2 I*w^2
KE(translational)=1/2 m V^2

now just pick an arbitrary R and m and put both equations in common terms; hint use w=vr and your other eqn I=mR^2. That should take care of probllem 1, but finish the other problem first. Mutitasking is good but not in physics!:smile:
 

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