The correct option is (d).
Explanation
An artificial satellite orbiting the Earth is essentially in a state of continuous free fall. Its stable orbit is the result of a precise balance between its tangential velocity (inertia) and the gravitational force exerted by the Earth. This gravitational force acts as a centripetal force, which is necessary to maintain circular or elliptical motion.
Detailed Analysis:
- Option (a) is Incorrect: The Earth's gravitational field extends infinitely, weakening with distance according to the inverse-square law ($1/r^2$). It is significant at the altitude of satellites and is the primary force governing their motion.
- Option (b) is Incorrect: The gravitational attraction of the Moon is negligible for a satellite in a typical Earth orbit compared to Earth's pull. It does not neutralize Earth's gravity; if it did, the satellite would leave its orbit.
- Option (c) is Incorrect: The necessary tangential speed is imparted by the launch vehicle (rocket) during orbital injection. Gravity does not provide this speed; it acts upon the object once it is in motion.
- Option (d) is Correct: According to Newton's laws, a force applied to a mass creates acceleration. The gravitational attraction of the Earth acts as the centripetal force, providing the necessary centripetal acceleration directed towards the center of the Earth. This acceleration constantly changes the direction of the satellite's velocity, curving its path to match the curvature of the Earth, thereby keeping it in orbit.
Key Takeaway:
Satellites do not fall to the ground because the Earth's gravitational attraction provides the necessary centripetal acceleration to keep them falling "around" the Earth rather than "into" it.