Why do particles with different masses share the same average kinetic energy?

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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...