Understanding Energy and Work Done

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Discussion Overview

The discussion revolves around the concepts of energy, work done, and the implications of collisions in a physics context. Participants explore the relationship between energy transfer, work, and the effects of friction and acceleration, with a focus on theoretical scenarios involving a falling rock and a pillar.

Discussion Character

  • Exploratory
  • Technical explanation
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • One participant asserts that energy is the capacity to do work and questions what happens to energy that is not used to perform work when a rock impacts a pillar.
  • Another participant agrees with the first and discusses the concept of a perfectly inelastic collision, noting that kinetic energy is lost as heat and sound, while momentum is conserved.
  • A question is raised about how to calculate the effect of acceleration on the percentage of useful work done.
  • A response suggests using Newton's second law and provides a formula for calculating work done, while noting that this method introduces uncertainty based on the assumption of an optimal amount of work.
  • One participant reiterates the point about energy loss during impact and raises a concern about the scenario where the pillar does not move, questioning whether this results in zero work done against friction.

Areas of Agreement / Disagreement

Participants generally agree on the principles of energy conservation and the effects of collisions, but there are competing views regarding the implications of friction and the conditions under which work is done, particularly in scenarios where the pillar does not move.

Contextual Notes

There are unresolved assumptions regarding the definitions of work and energy in the context of friction and motion, as well as the conditions under which energy is dissipated during impacts.

Who May Find This Useful

This discussion may be useful for students and enthusiasts of physics, particularly those interested in the concepts of energy, work, and mechanics in collision scenarios.

sgstudent
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Energy is the capacity to do work. So if I have energy I can do work. But if a rock has 100J from falling down a building to push a pillar into the ground, it might not have enough energy to have any work done to push it in. So what happens to that 100Js? Ignoring air resistance. Since energy can neither be destroyed or created so I'm unsure where energy that isn't used has gone. I'm theorizing that heat and sound is produced from the impact and that's the energy dissipated but I'm not completely sure about it. I'm unsure if the friction of the pillar constitutes into this. But then again work done against friction also requires a distance which is 0 when the pillar doesn't move. Thanks for the help! :)
 
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yup, you are right. upon impact(assume rock+pillar stick together ie. perfectly inelastic collision, momentum conserved, kinetic energy not conserved, lost as heat and sound). also, work done against friction between the sides of the pillar against the ground(as your pillar gains momentum and hence velocity).
 
how would you calculate the effect of acceleration on the precentage of useful work done?
 
You would use Newton's second law. The same rock from before is traveling down with a magnitude and direction of mass * acceleration.
sumF=ma,
W=FdcosT
W=dmacosT, substituting.
for some arbitrary acceleration, the work done is given by the equation.. If you want to use percentages, divide this number by the necessary work to achieve an optimal result, and multiply by 100. This method will however lead to some level of uncertainty constrained by the assumption that some optimal amount of work is the minimum amount of work needed in a system.
 
jester1989 said:
yup, you are right. upon impact(assume rock+pillar stick together ie. perfectly inelastic collision, momentum conserved, kinetic energy not conserved, lost as heat and sound). also, work done against friction between the sides of the pillar against the ground(as your pillar gains momentum and hence velocity).
But what if the pillar doesn't move. Then won't there be zero work done again friction?
 
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Last edited:

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