Correct Option
The correct option isIt acts in the direction opposite to the velocity.
Explanation
Acceleration is a vector quantity defined as the rate of change of velocity with respect to time. In linear motion (motion along a straight line), the relationship between the direction of velocity and acceleration determines whether the speed of the object increases or decreases.
Detailed Analysis
- It acts in the same direction as velocity. is incorrect: When acceleration acts in the same direction as velocity, the speed of the object increases. This is referred to as positive acceleration.
- It acts in the direction opposite to the velocity. is correct: When acceleration acts in the direction opposite to the velocity, it opposes the motion. This causes the speed of the object to decrease over time. This phenomenon is technically termed negative acceleration, deceleration, or retardation.
- The object is moving in a circular path. is incorrect: Motion in a circular path involves a continuous change in direction. While there is acceleration (centripetal), the term "retardation" specifically refers to a decrease in speed in linear contexts, not merely the geometry of the path.
- The object starts from a state of rest. is incorrect: When an object starts from a state of rest, its velocity increases from zero. This requires a positive acceleration in the direction of motion to initiate movement.
Key Takeaway
Retardation (or negative acceleration) occurs strictly when the acceleration vector is directed opposite to the velocity vector, resulting in a reduction of speed.