- #1
eurekameh
- 209
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I don't understand why the force is acting through a distance of 1.2pi, even though the center of the disk clearly moves a distance of 0.6pi.
Work-Energy: Force Acting Through 1.2pi Despite 0.6pi Move
- Thread starter eurekameh
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- Work-energy
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Homework Help Overview
The discussion revolves around a work-energy problem involving a disk and the forces acting on it. Participants are exploring the relationship between the distance the disk moves and the distance over which the force is applied, specifically addressing the implications of translational and rotational motion.
Discussion Character
- Exploratory, Conceptual clarification, Assumption checking
Approaches and Questions Raised
- Participants are questioning why the force acts over a distance of 1.2pi while the disk moves only 0.6pi. There are discussions about the unwinding cord and its effect on the force application. Some participants are considering the role of moments about the center of mass and their contribution to work done and kinetic energy.
Discussion Status
The discussion is active, with participants raising various points about the mechanics involved. Some have identified the types of kinetic energy at play, while others are probing deeper into the implications of the force and moment relationships. There is no explicit consensus, but several productive lines of inquiry are being explored.
Contextual Notes
Participants are working within the constraints of a homework problem, which may limit the information available and the assumptions that can be made regarding the system's dynamics.
I don't understand why the force is acting through a distance of 1.2pi, even though the center of the disk clearly moves a distance of 0.6pi.
- #2
gneill
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The cord is unwinding. So the length of cord between where it meets the disk and whatever it is that's pulling on the cord will grow longer. Clearly whatever is applying the force to the free end of the cord has to mover further than the disk's center.
- #3
eurekameh
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Isn't the force also causing a moment about the center of mass? Shouldn't this contribute to the work done?
- #4
gneill
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eurekameh said:
Doing work results in a change in energy, in this case a change in the energy of motion. Can you identify where the energy of motion is going to end up in this case?
- #5
eurekameh
- 209
- 0
Translational and rotational kinetic energy. The force moves through a distance of 1.2pi. But it is also causing a moment through an angle of 2pi. Shouldn't this moment through an angle also be contributing to the total kinetic energy (translational and rotational) of the disk?
- #6
gneill
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eurekameh said:
You've identified translational and rotational kinetic energies to be where the work energy ends up. That's good. The solution included with the question deals with both.