1. Not finding help here? Sign up for a free 30min tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Proton passes the Milky Way galaxy, find its energy?

Tags:
  1. Oct 11, 2005 #1
    for the following question:
    In its own frame of reference, a proton takes 5min to cross the Milky Way galaxy, which is about 10^5 light-years in diameter.
    What is the approximate energy of the proton in electronvolts?

    my problem:
    v*5*60=(10^5)*3*(10^8)*[1-(v^2/c^2)]
    however, i can't calulate v on the calculator, because v is too small...
    i was trying to use E=(1/2)mv^2, where m is the photon rest mass...
    is that right?

    @@a
     
  2. jcsd
  3. Oct 11, 2005 #2

    Tom Mattson

    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    This looks like algebraic soup! Why, oh why, are you combining these quantities together in this way? From what equation are you working?

    It looks like:

    [tex]vt=\frac{Dc}{\gamma ^2}[/tex]

    where [itex]v[/itex] is the proton speed in the galaxy frame, [itex]D[/itex] is the galactic radius in the galaxy frame, and [itex]t[/itex] is the travel time in the proton frame.



    No, it's not right. The photon rest mass is zero.
     
    Last edited: Oct 11, 2005
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?



Similar Discussions: Proton passes the Milky Way galaxy, find its energy?
  1. Mass of the Milky Way (Replies: 1)

Loading...