A (yet-to-be-built) spacecraft starts from Earth moving at constant speed to (yet-to-be-discovered) planet Retah, which is 25.2 lt · h away from Earth. It takes 50.4h (according to an Earth observer) for the spacecraft to reach this planet. [A lt-h is a light-hour.] Assuming the clocks are synchronized beginning of the journey, what is the time elapsed in the spacecraft's proper frame of reference for this one-way journey? Answer in units of h.
Answer: Time elapsed in the... View the full answer