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Homework Help: Calculating rest mass and energy (in an inertial frame)

  1. Feb 12, 2017 #1
    1. The problem statement, all variables and given/known data
    A particle is accelerated so it has a total energy of 10GeV measured in the accelerator’s rest frame. The particle's momentum is 8GeV/c in the same frame. Calculate...

    a.) Rest mass of the particle
    b.) Energy in an inertial frame in which its momentum is 6GeV/c
    c.) The speed of the this reference frame relative to the accelerator's rest frame.

    2. Relevant equations

    http://www.sciweavers.org/upload/Tex2Img_1486938602/render.png [Broken]

    3. The attempt at a solution

    Using the stated relevant equation, I found the rest mass to be equal to 6 GeV/c^2, and then the energy in the inertial frame to be 0. I'm not sure if these are right, especially b! So I'm worried I may have over simplified things a little.

    I'm not entirely sure how to do c. Could I attempt to rearrange the relativistic momentum equation using transforms?

    Any guidance would be much appreciated...
    Last edited by a moderator: May 8, 2017
  2. jcsd
  3. Feb 12, 2017 #2


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    There's a misprint in this equation. But I don't think it affected your result for (a), which I think is correct.

    You must have made a mistake for part (b). Can the relativistic total energy of a free particle ever be zero?

    I'd have to see more detail of what you mean here.
  4. Feb 12, 2017 #3
    Yeah I was confused with b. I assumed there should always be energy as a result of mass. So I can't simply plug in my rest mass and the given momentum value for the specified inertial frame?
  5. Feb 12, 2017 #4


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    Yes, the minimum possible energy is the rest energy associated with the mass.
    Yes, you can do that. :smile: But you shouldn't get zero for the total energy.
  6. Feb 12, 2017 #5
    Oh I put a minus! Why?! xD Okay...

    http://www.sciweavers.org/upload/Tex2Img_1486942686/render.png [Broken]

    Therefore E = 8.49GeV
    Last edited by a moderator: May 8, 2017
  7. Feb 12, 2017 #6
    For c. I was thinking of using p = γmv... But using a velocity transform

    http://www.sciweavers.org/upload/Tex2Img_1486943107/render.png [Broken]

    I'm not entirely sure how applicable it would be. But I'll have a play and come back in the morning. Come to think of it I don't think it would work with the available info, without some serious playing around. But I'll come back in the morning and see what I've got. Thank you so far
    Last edited by a moderator: May 8, 2017
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