Correct Option
The correct option is (c).
Explanation
Galileo Galilei conducted experiments using inclined planes to understand the nature of motion. His observations challenged Aristotelian physics and laid the groundwork for the concept of inertia, which was later formalized as Newton's First Law of Motion.
Statement-wise Analysis
- Statement 1 is Incorrect. When a marble rolls down an inclined plane, the component of gravitational force acts in the direction of motion. This causes the marble to accelerate, meaning its velocity increases as it descends.
- Statement 2 is Correct. When a marble climbs up an inclined plane, it moves against the component of gravitational force. This opposing force causes the marble to decelerate, resulting in a decrease in velocity.
- Statement 3 is Correct. On a horizontal plane, gravity acts perpendicular to the direction of motion and does not accelerate or retard the object. Galileo reasoned that in an ideal case where friction is absent, there is no net force to oppose the motion. Consequently, the marble would continue to move with a constant velocity forever.
Key Takeaway: An object requires no external force to maintain its motion in a straight line with constant speed if resistive forces like friction are absent. This property is known as inertia.