1. The problem statement, all variables and given/known data Studying Special Relativity at the moment, and having a little trouble getting to grips with it. I've got stuck on this question, and was wondering if anyone could clear it up for me? Here's the question: "A rocket is travelling at 0.6c, v, along the x-axis relative to you. It fires a missile in the y-axis (perpendicular to the rocket in the rocket's reference frame) at 0.7c relative to you. What speed and at what angle to the x-axis do you see the missile travelling?" I think you have to use the Lorentz transformations for velocity, but I'm not sure. 2. Relevant equations I think: ux' = (ux-v)/(1-uxv/c^2) and: uy' = uy/(gamma*(1-uxv/c^2)) 3. The attempt at a solution I think you have to use the Lorentz transformations for velocity, but I'm not sure. I'm just getting confused with which reference frames to choose for the rocket, and what the variables "ux", "ux'" and "v" are and how to put them in.