A mass M is dragged by a pulley on a horizontal plane by a force anti-parallel to its displacement. The work done in pulling the mass M is

In physics, work done is defined as the product of the force magnitude, the displacement magnitude, and the cosine of the angle (θ) between the force and displacement vectors. When a force is anti-parallel to the displacement, the angle θ is 180 degrees. Since the cosine of 180 degrees is -1, the resulting work done is negative. This occurs because the force acts in the opposite direction to the motion, effectively removing energy from the system or opposing the displacement. Common examples of negative work include the force of friction acting on a sliding object or the force applied when braking a moving vehicle. In the given scenario, dragging a mass with a force anti-parallel to its displacement results in negative work because the force vector and displacement vector point in opposite directions.