Astronomy Practice Exam

What is escape velocity?

1. The speed needed to reach orbit

2. The speed needed for a rocket to escape the pull of the Earth's gravity

3. The speed that objects fall back to Earth

4. The maximum speed of a spacecraft

The correct answer is: The speed needed for a rocket to escape the pull of the Earth's gravity

Escape velocity refers to the minimum speed an object must have to break free from the gravitational attraction of a celestial body without further propulsion. In the case of the Earth, this velocity is approximately 11.2 kilometers per second (about 25,000 miles per hour). Choosing the notion of escape velocity as the speed needed for a rocket to escape the pull of Earth's gravity highlights that this speed allows an object to overcome gravitational forces and other potential energy barriers that would otherwise pull it back. Once an object reaches this velocity, it can continue moving away from the Earth into space without being drawn back down. This concept is pivotal in understanding space travel and the dynamics of rocket launches. While the speed needed to reach orbit is a related concept, it is typically lower than escape velocity because maintaining an orbit involves a balance between gravitational pull and centripetal force, rather than simply overcoming gravity. Similarly, the speed that objects fall back to Earth does not pertain to escape velocity, as this is a speed that is reached when an object returns to the gravitational influence of the planet, rather than escaping it. The maximum speed of a spacecraft is also not directly connected to escape velocity, as spacecraft can reach various speeds depending on their trajectories and propulsion systems, which do