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Statement of a problem № 41607

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The cosmic rays of highest energy are protons that have kinetic energy on the order of 1013 MeV. (a) How long would it take a proton of this energy to travel across the Milky Way galaxy, having a diameter ~105 ly, as measured in the proton’s frame? (b) From the point of view of the proton, how many kilometers across is the galaxy?




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