Is this a misprint in my SR homework?

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SUMMARY

The forum discussion centers on a homework problem involving relativistic energy and momentum transformations for an electron moving at a specified energy of 3mc² and momentum magnitude of √8mc. Participants express confusion regarding the concept of proper velocity and the implications of relativistic momentum calculations. The key equations discussed include the relativistic velocity equation dx/dτ = γdx/dt and the relationship between mass and momentum m(γ(dx/dt)) = √8mc. The consensus is that the problem's wording may lead to misunderstandings about the electron's proper velocity.

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sigma_
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Homework Statement


"In frame of reference S, an electron moving along the x-axis has
energy 3mc2 and momentum magnitude √(8)mc
Use the transformations of energy and momentum to find the energy and momentum magnitude observed in
frame S′ moving with speed 4c/5 relative to S in the positive x-direction."


Homework Equations


How can the electron have a proper velocity of c?

If relativistic velocity is dx/dτ = γdx/dt, and relativistic momentum is simply the mass time the relativistic velocity, how is m(γ(dx/dt)) = √8mc?


The Attempt at a Solution


I solved the problem correctly, I am just unsure of a detail in the wording of the problem.
 
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Hello

sigma_ said:
How can the electron have a proper velocity of c?

How do you get that the electron has a proper velocity of c?

If relativistic velocity is dx/dτ = γdx/dt, and relativistic momentum is simply the mass time the relativistic velocity, how is m(γ(dx/dt)) = √8mc?

What is it about m(γ(dx/dt)) = √8mc that you find disconcerting?
 

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