1. The problem statement, all variables and given/known data Hi everybody. I was tasked with the following exercice: Two identical protons of energy 7TeV collide head on. Which is the total energy of the system? How is compared this energy with the one of an Airbus 320 which mass is t50*10^6Kg at a speed of 600Km/h? How many photons do we need for the total energy was equivalent to the Airbus? 2. Relevant equations I am considering that the speed of light is 1 and it has no units. Relativistic energy: E=Sqrt(m^2+p^2) 3. The attempt at a solution To the first question: If both photons have the same energy, the total energy of the system must be 14 TeV; exactly twice the energy of the photon. To the second question: Here, I write the aeroplane's energy as E=Sqrt(m^2+(m*v)^2), qhere v is the speed (all in the SI). So E=Sqrt((50*10^4)^2+((50*10^4)*(166.67))^2) =8.3*10^7J. On the other hand 1J=1/(1.602*10^19)eV; so E =5.2*10^25eV=5.2*10^11Tev. To the third question: 5.2/7=0.74; so we need 7.4*10^10 protons to obtain the same energy. Can someone please tell me if I have calculated the energy of the aeroplane properly? Thanks for reading.