In an experiment, two protons are shot directly toward each other, each moving at half the speed of light relative to the laboratory.
(a) What speed does one proton measure for the other proton?
(b) What would be the answer to part (a) if we used only non-relativistic Newtonian mechanics?
(c) What is the kinetic energy of each proton as measured by (i) an observer at rest in the laboratory and (ii) an observer riding along with one of the protons?
(d) What would be the answers to part (c) if we used only non-relativistic Newtonian mechanics?