6) a) A skydiver leaps from a plane 5000 meters above the ground (with no initial velocity). The skydiver weighs 50 kg and falls under the influence of gravity. Air resistance is proportional to their velocity, but before they pull the parachute cord their air resistance is 10 N-sec/m, and after they pull it changes to 100 N-sec/m. The sky diver is instructed to pull the cord 80 seconds after leaping from the plane. How fast is the skydiver falling 5 seconds after they leap? b) If the skydiver pulls the cord 80 seconds after leaping from the plane, how many seconds after pulling the chord does it take for the skydiver to land?