a 10 kg migratory swan cruises at 20 m/s. a calculation that takes into account the necessary forces shows that this motion requires 200 w of mechanical power. if we assume an efficiency similar to humans, a reasonable assumption, then the metabolic power of the swan is significantly higher than this. the swan doesn't stop to eat during a long day of flying; it gets the energy it needs from fat stores. assume an efficiency similar to humans. after 12 hours of flight, what fraction of its body mass does it lose?