Is the Assumption of Equal KE for Particles Justified in Physics?

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Discussion Overview

The discussion revolves around the justification of assuming equal kinetic energy (KE) for particles with different masses in a physics context, particularly in relation to an exam question and its mark scheme. Participants explore the implications of this assumption and its relation to temperature and average kinetic energy.

Discussion Character

  • Debate/contested
  • Conceptual clarification
  • Homework-related

Main Points Raised

  • One participant questions the validity of assuming equal average kinetic energy for particles of different masses, suggesting that this contradicts the principle that different masses would have different kinetic energies.
  • Another participant clarifies that the average kinetic energy refers to the average of all particles, implying that while individual particles may have different kinetic energies, the average can be the same.
  • A participant points out that the lighter particle would have a higher velocity to maintain the same kinetic energy as a heavier particle.
  • One contribution emphasizes that temperature is related to the average kinetic energy of a large number of particles, rather than the kinetic energy of individual particles.
  • Some participants express skepticism about the clarity of the exam question, suggesting it may be poorly worded.

Areas of Agreement / Disagreement

Participants generally do not reach a consensus on the justification of the assumption of equal kinetic energy for different mass particles. Multiple competing views remain regarding the interpretation of the average kinetic energy and its implications.

Contextual Notes

There are unresolved questions about the assumptions underlying the exam question and the definitions of average kinetic energy and temperature in this context.

elemis
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http://www.xtremepapers.com/papers/CIE/Cambridge%20International%20A%20and%20AS%20Level/Physics%20(9702)/9702_w10_qp_43.pdf

The mark scheme says we can assume that each particle has an AVERAGE KE = 1.2*10-14.

How can this be correct ? Both particles have different masses and hence would have different KEs ?
 
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They mean the average ke of the particles. All Exams have at least one badly worded question in them. I think it is a government requirement.
 
sophiecentaur said:
They mean the average ke of the particles. All Exams have at least one badly worded question in them. I think it is a government requirement.
Could you elaborate ? I don't quite understand what you mean ?
 
Both particles have different masses but the same kinetic energy because the lighter particle is moving faster.
 
A particle doesn't have a temperature. It will have KE. The temperature is the average KE of all the (large number of) particles.
The average is over all the particles rather the average of 'each' particle (over all time?).
 
The whole question may tell us which way the examiner is thinking.
 
sophiecentaur said:
The whole question may tell us which way the examiner is thinking.
The question begins on page 6...
 

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