Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Homework Help: Modern Physics I: Find time from energy

  1. Sep 17, 2010 #1
    1. The problem statement, all variables and given/known data
    A particle with a rest energy of 2400 MeV has an energy of 15 GeB (15x10^9 eV). Find the time in Earth's frame of reference necessary for this particle to travel from Earth to a star four light-years distant.

    2. Relevant equations

    3. The attempt at a solution

    I thought about using the rest energy and total energy to find the Kinetic Energy. After that I used the velocity I found and used that to find the time. Is this a good start?
  2. jcsd
  3. Sep 17, 2010 #2
    That's how I would start it. You might also be able to keep things in terms of c, since the distance is in terms of c. That way you don't need to convert back and forth from m/s.
  4. Sep 17, 2010 #3
    Ok thanks. I tried to work it out and this is what I got. I ended up getting a value of 1.26E10 eV for kinetic energy. Using that, I got the ratio v/c to equal .987. I used that to get a time of 4.05 light years for the answer. Any thoughts? Thanks in advance.
  5. Sep 18, 2010 #4
    I worked on this problem again today, but couldn't come up with any other way to think about it. If anyone can confirm my above thinking, I will be appreciative.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook