4. a) (10 points) The gold medal winner in Olympic downhill skiing manages to descend the course at 0.87c. How do they perceive the length of the course (in km), compared to the measurement of 3 km made by the organizers? b) (10 points) A light beam fired from the start passes the skier halfway down the run. How fast does the skier measure the light as moving (in m/s)? Why?