As a space ship from earth goes toward the moon, the force it exerts on the earth

As a space ship from earth goes toward the moon, the force it exerts on the earth

• A. decreases
• B. increases
• C. remains the same
• D. none of these

Answer: (A)

The force between two masses follows the inverse-square law: F = G m_E m_s / r^2. As the spaceship moves away from Earth toward the Moon, the distance r between them increases, so the gravitational attraction between Earth and the ship decreases. By Newton’s third law, the ship feels the same magnitude of force from Earth, and Earth feels the same magnitude from the ship, so that force on Earth also weakens as the ship gets farther away. If the distance were doubled, the force would drop to one-quarter, illustrating the strong dependence on distance.

The force between two masses follows the inverse-square law: F = G m_E m_s / r^2. As the spaceship moves away from Earth toward the Moon, the distance r between them increases, so the gravitational attraction between Earth and the ship decreases. By Newton’s third law, the ship feels the same magnitude of force from Earth, and Earth feels the same magnitude from the ship, so that force on Earth also weakens as the ship gets farther away. If the distance were doubled, the force would drop to one-quarter, illustrating the strong dependence on distance.