Q. Determine the mass of Earth from the period T and the radius r of the Moon's orbit about the Earth. T=27.3 days and r=3.82E5 km. Assume the Moon orbits the center of Earth rather than the center of mass of the Earth-Moon system.
Q. A positron is a particle of "antimatter"; it has the same mass as an electron (9e-31 kg), but its charge is positive instead of negative. At research facilities such as the Cornell Electron Positron Storage Ring at Cornell University in New York, high energy beams of positrons can be produced.
When a positron encounters an electron, the two particles annihilate each other, and produce two high energy photons (gamma rays), which travel away from each other.
Suppose that a positron traveling at a speed of 0.95c collides head on with an electron traveling at the same speed.
What is the sum of the energies of the two photons which are produced when the positron and the electron annihilate?
sum of photon energies = J?