4. The escape velocity (minimum velocity to escape the Earth's gravitational potential) for a 100-kg object on Earth is about 11 km/s. What is the escape velocity of a 50-kg object on the surface of Earth? (A) 11 km/s (B) 22 km/s (C) 5.5 km/s (D) 44 km/s (E) 2.75 km/s