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?