A plane is traveling at a steady speed of 250 km/hr relative to the ground. An hour into the flight a passenger on the plane observes the plane pass Superman casually standing still in the sky talking on his cell phone. In a half hour the passenger then sees Superman passing by at a speed of 300 km/hr (also relative to the ground). a. Using Galilean relativity: according to the observer on the plane how fast is Superman moving relative to the plane?

b. Now find the answer to (a) using special relativity. How different is it?

c. Now the observer on the plane realizes that Superman is trying to stop a spaceship entering Earth's atmosphere. He sees Superman flying away from the Earth at a half speed of light (c) and the unknown object flying towards Earth at half the speed of light. From the perspective of the unknown object, how fast is Superman flying?