1. The problem statement, all variables and given/known data Two objects fly toward you, one from the east with speed u, and the other from the west with speed v. Is it correct that their relative speed, as measured by you, is v+u? Or should you use the velocity addition formula, V=(u+v)/(1+uv/c2)? Is it possible for their relative speed, as measured by you, to exceed c? 2. Relevant equations It is more conceptual then anything, at least that's supposed to be it's purpose. 3. The attempt at a solution The wording of the problem is very confusing to me... but here is an explanation. If I consider the object from the other frame to be a moving frame S' then the velocity formula needs to be used, especially when their speeds are approaching C. Secondly it is possible for their relative speed, as measured by me, to be greater then C. This is not to mean that they themselves are exceeding the speed of light, but the speed of one particle RELATIVE to the other particle ACCORDING to me is greater then c. To measure an object according to myself and relative to myself, with a speed greater than c is not permissible due to Einsteins second postulate.