1. The problem statement, all variables and given/known data You observe a lead brick with a rest mass of 27 kg. What is its apparent mass if it is moving away from you at 0.73c? The speed of light is 3e8 m/s. Answer in units of kg. What if you are moving toward it at -0.73c? 2. Relevant equations 3. The attempt at a solution My Physics teacher hasn't taught us any equations yet to help solve these types of problems. He relies on us to use an "online calculator" that is currently not working on my computer.