1. The problem statement, all variables and given/known data 1. A spaceship travelling away from earth with a speed of 0.6c as measured by an observer on earth. The rocket sends back a light pulse back to earth every 10 minutes as measured by a clock in the spaceship. How far does the spaceship travel between each light pulses as measured by: a) the observer on earth and b) someone on the spaceship? 2. An electron is moving at a constant velocity of 0.90c with respect to a lab observer X. Another observer Y is moving at a constant velocity of 0.50c with respect to X in a direction opposite to that of the electron in X's reference frame. What is the mass of the electron as measured be Y? 3. Protons are accelerated from rest through a potential difference of 8.0E8 V. Calculate as measured in the laboratory frame of reference after acceleration the proton's mass, velocity, momentum and total energy. 2. Relevant equations Lorentz transformation? 3. The attempt at a solution 1. a) I first found time t passed on earth between pulses and simply used d = (t)(0.6c). But it didn't work. And I haven't a clue how to do the second part. The other ones I don't have a single clue.