Correct Option
The correct option isThe object returns to its initial position.
Explanation
Motion is described using two distinct physical quantities: distance and displacement. Distance is a scalar quantity representing the total length of the path covered by an object. Displacement is a vector quantity defined as the shortest straight-line distance from the initial position to the final position, pointing from the start to the end.
Detailed Analysis:
- The object moves in a straight line without reversing. is Incorrect: When an object moves in a straight line without reversing direction, the magnitude of displacement is exactly equal to the distance travelled. Since the distance is non-zero, the displacement must also be non-zero.
- The object returns to its initial position. is Correct: Displacement depends solely on the change in position ($\Delta x = x_{final} - x_{initial}$). If an object returns to its initial position, the final coordinate is identical to the initial coordinate. Therefore, the vector difference is zero, resulting in zero displacement, even though the total path length (distance) is positive.
- The object moves with variable speed. is Incorrect: Variable speed refers to the change in the magnitude of velocity over time. It does not determine the final position of the object relative to the start. An object can have variable speed and still have a large non-zero displacement.
- The object undergoes negative acceleration. is Incorrect: Negative acceleration (often termed retardation when opposing motion) implies a change in velocity. While it may cause an object to stop or reverse, it does not automatically imply that the object has returned to the starting point.
Key Takeaway:
Displacement is path-independent and relies only on the initial and final positions. For any closed path (where the start and end points are the same), the displacement is always zero, whereas the distance is the total circumference or path length covered.