A4.0 x 10^10 kg asteroid is heading directly toward the center of the earth at a steady 20 km/s. to save the planet, astronauts strap a giant rocket to the asteroid perpendicular to its direction of travel. the rocket generates 5.0 x 10^9 n of thrust. the rocket is fired when the asteroid is 4.0 x 10^6 km away from earth. you can ignore the earth’s gravitational force on the asteroid and their rotation about the sun. if the mission fails, how many hours is it until the asteroid impacts the earth?