Correct Option
The correct option isIt is negative and decreases the kinetic energy.
Explanation
Work done ($W$) by a constant force is defined mathematically as the product of the magnitude of the force ($F$), the magnitude of displacement ($s$), and the cosine of the angle ($\theta$) between them: $W = F s \cos \theta$. The Work-Energy Theorem further establishes that the net work done on an object is equal to the change in its kinetic energy.
Detailed Analysis
- Sign of Work Done: In this scenario, the force is applied in the direction opposite to the object's motion (displacement). Therefore, the angle $\theta$ between the force vector and the displacement vector is $180^\circ$. Since $\cos 180^\circ = -1$, the work done is calculated as $W = -Fs$. This indicates that the work done is negative.
- Effect on Kinetic Energy: A negative work value implies that energy is being removed from the system. According to the Work-Energy Theorem, this negative work results in a decrease in the object's kinetic energy. Physically, the opposing force acts as a retarding force, causing the object to decelerate.
Key Takeaway: When a force acts opposite to the direction of displacement (angle = $180^\circ$), the work done is negative, which results in a reduction of the object's kinetic energy.