Centripetal Force Directs Satellite's Motion

Steps:

• Satellite orbits at constant speed, requiring centripetal acceleration toward planet P's center.
• Newton's second law states resultant force equals mass times centripetal acceleration, directed inward.
• Gravitational force from P provides this resultant force, radially toward the center.
• Direction D aligns with this inward radial path.

Why D is correct:

• In uniform circular motion, the resultant force must be centripetal, toward the center, as per $F = \frac{mv^2}{r}$, matching gravity's direction.

Why the others are wrong:

• A: Resultant force zero implies no acceleration, but circular motion requires centripetal acceleration.
• B: Direction B likely tangential, which would change speed, not sustain constant-speed orbit.
• C: Direction C likely outward or perpendicular, opposing the needed inward pull for orbit.

Final answer: D