Special Relativity, energy and momentum

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SUMMARY

The discussion focuses on calculating the total kinetic energy of two protons, each moving at 0.5c, in two different reference frames: S' and S. The kinetic energy formula used is K=(mc^2/sqrt(1-(v/c)^2))-mc^2. To find the velocity of the second proton in frame S, participants emphasize the importance of using the relativistic velocity addition formula instead of classical summation, which incorrectly suggests a speed of light. Additionally, applying Lorentz transformations is recommended for converting energy and momentum values between frames.

PREREQUISITES
  • Understanding of special relativity concepts
  • Familiarity with the kinetic energy formula in relativistic physics
  • Knowledge of the relativistic velocity addition formula
  • Ability to perform Lorentz transformations
NEXT STEPS
  • Study the derivation and application of the relativistic kinetic energy formula
  • Learn the relativistic velocity addition formula in detail
  • Explore Lorentz transformations and their implications in physics
  • Practice problems involving energy and momentum calculations in different reference frames
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Students and educators in physics, particularly those studying special relativity, as well as anyone interested in advanced concepts of energy and momentum in relativistic contexts.

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Homework Statement



In reference frame S', two protons, each moving at .5c, approach each other head on. A) Calculate the total kinetic energy of the two protons in frame S'. B) Calculate the total kinetic energy of the protons as seen en reference frame S, which is moving with one of the protons.

Homework Equations



K=(mc^2/sqrt(1-(v/c)^2))-mc^2

The Attempt at a Solution


I have no attempt. I have no idea where to start.
 
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Well I will assume you know the answer to A, since you wrote out the equation. And in B, you know the velocity of one of the protons is 0. To get the velocity of the other proton, instead of summing the velocities classically which would get you the 2nd proton moving at the speed of light, c (which is impossible). You would add the velocities relativistically:

http://en.wikipedia.org/wiki/Velocity-addition_formula
 
You could also calculate the energy and momentum of the protons in the S' frame and then use a Lorentz transformation to find their values in the S frame.
 

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