Solving Momentum Equalization of Electron and Proton

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SUMMARY

The discussion centers on calculating the speed of a proton required to match the momentum of an electron traveling at 0.14c. The initial attempt yielded a momentum calculation of 22873.91 m/s, while the correct value is 23139.3 m/s. The discrepancy arises from the need to apply the concept of relativistic momentum, defined by the equation p = mv / √(1 - (v²/c²)), which accounts for relativistic effects as the speed approaches the speed of light. Participants emphasized the necessity of understanding Special Relativity concepts, including Lorentz transformations and the gamma factor, to solve the problem accurately.

PREREQUISITES
  • Understanding of relativistic momentum equations
  • Familiarity with Special Relativity concepts, including Lorentz transformations
  • Basic algebra skills for manipulating equations
  • Knowledge of the speed of light (c) and its significance in physics
NEXT STEPS
  • Study the derivation and application of the relativistic momentum equation p = mv / √(1 - (v²/c²))
  • Learn about Lorentz transformations and their implications in physics
  • Explore the concept of time dilation and length contraction in Special Relativity
  • Review Einstein's theory of relativity and its foundational equations, including E = mc²
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Students studying physics, particularly those tackling problems in Special Relativity, as well as educators seeking to clarify the application of relativistic concepts in momentum calculations.

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Homework Statement


An electron has a speed of v = 0.14c. At what speed will a proton have a momentum equal to that of the electron?

Homework Equations


p=mv


The Attempt at a Solution


MeVe = MpVp where p=proton and e=electron
so: MeVe/Mp=Vp
Me = 9.109 X 10^-31 kg
Mp = 1.672 X 10^-27 kg

Plugging this information in gives me an answer of 22873.91 m/s but the correct answer is 23139.3 m/s. What am I doing wrong? Thanks in advance for any help!
 
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Does the word "relativistic" mean anything to you? Has the name Einstein come up in class?

And what's the deal with all those digits? If the speed is given as ".14c" the correct answer should be 23,000 m/s .
 
Last edited:
We briefly talked about einstein and E = mc^2 but the professor didnt really go over it...I also understand that .14c means .14 X 3e8...but I don't understand why the answer should be 23,000...any hints?
 
"Breifly went over E=mc^2"?

You mean "Lorenzian Transformation" "time dialation" "length contraction"
"gamma factor" and "mass increase" were never discussed? If not, then there is no business assigning this problem. You do not need "hints" you need about two weeks worth of Special Relativity lessons.
 
Like I said, briefly. We never really talked about these...the prof just gave us equations on the board and told us "use these to solve the homework, you won't be tested on them"
 
Also, the homework is due tomorrow and this is the only problem I have left...
 
What a waste of time. "Just do the problems without knowing what's going on" right? I'm sorry for you.

Relativistic momentum: find the equation that resembles the following:

p=(mv)/SQRT[1-(v^2/c^2)]. You are in for an algebraic workout since v appears in two places.

Edit: That looks horrible. Here's the latex version

p=\frac{mv}{\sqrt{1-\frac{v^{2}}{c^{2}}}}$

well that's not looking great either.
 
Last edited:
got it...thanks!
 

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