1. The problem statement, all variables and given/known data This is just a short response problem on my homework. It asks: "If a particle is moving at a relativistic velocity, is the following equation still valid? |q|vB = mv2/r If the particle is an electron, what is the value of the mass?" (electron mass = 9.1094x10-31) 2. Relevant equations |q|vB = mv2/r 3. The attempt at a solution I would think that the equation still applies. Velocity is relative so it does not change when the frame of reference changes. Is that correct? Would I also just use the given electron mass for the mass? Maybe I'm thinking too much... Would .511MeV/c2 work too? One side question. Would the radius be a contracted length? How would that be calculated? Any help is greatly appreciated. Thank you so much!