UPSC NDA 2 2021 General Ability Solved Paper

A negative work is done when an applied force and the corresponding displacement S are anti-parallel to each other. The work W that a force F does on an object is the product of the magnitude F of the force, times the magnitude d of the displacement, times the cosine of the angle θ between them. In symbols, W=fd‌cos‌θ.
So, if angle is 180 degree, W will be negative.