Solving problem dealing with PE + KE WITHOUT mass values?

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Homework Help Overview

The discussion revolves around a problem related to the conservation of mechanical energy, specifically comparing the release heights of a solid sphere and a solid cylinder rolling down a ramp to achieve the same speed at the bottom. The original poster mentions a height of 13.7 cm for the sphere but indicates that this answer was marked incorrect.

Discussion Character

  • Exploratory, Conceptual clarification, Assumption checking

Approaches and Questions Raised

  • Participants discuss the relationship between potential energy and kinetic energy, including the contributions of translational and rotational kinetic energy. There are questions about the moment of inertia for different shapes and how it affects the problem. Some participants express confusion about the concepts presented.

Discussion Status

There is an ongoing exploration of the concepts of rotational dynamics and energy conservation. Some guidance has been offered regarding the moment of inertia and its relevance to the problem, but there is no clear consensus or resolution yet.

Contextual Notes

Participants are grappling with the implications of mass values and the differences in moment of inertia between the solid sphere and cylinder, which are critical to solving the problem. The original poster's misunderstanding of the initial feedback is also noted.

riseofphoenix
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A group of students perform the same "Conservation of Mechanical Energy" experiment that you performed in lab by allowing a solid sphere and then a solid cylinder to roll down the ramp. The solid sphere was released from a height of 13.7 cm. From what height hcylinder should the solid cylinder be released so that it has the same speed as the solid sphere when it reaches the bottom of the ramp?


I just said "13.7 cm" but I got marked as "INCORRECT"
Does anyone know the answer?
 
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Hint: how is the moment of inertia of a cylinder different than that of a sphere?
 
The initial potential energy at the top of the ramp transforms into kinetic energy at the bottom. The kinetic energy is the sum of the translational KE and the rotational one. The rotational energy depends of the moment of inertia, which depends on the shape.

ehild
 
Wait what?
Can you put that in an equation?
I have no idea what you just said :(
 
Have you studied rotational dynamics? Do you know what rolling means?

Try to read http://www.physics.ohio-state.edu/~gan/teaching/spring99/C12.pdf. Scroll down, there is an example about rolling down an incline.

ehild
 

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