A mass M is dragged by a pulley on a horizontal plane by a force anti-

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

zero
positive
infinite
negative
This question was previously asked in
UPSC NDA-1 – 2022
Work done (W) is calculated as the dot product of force (F) and displacement (d): W = F ⋅ d = |F| |d| cos(θ), where θ is the angle between the force vector and the displacement vector. The problem states that the force is “anti-parallel” to its displacement. This means the force and displacement vectors are in opposite directions, so the angle between them is 180 degrees. The cosine of 180 degrees (cos(180°)) is -1. Therefore, the work done is W = |F| |d| (-1) = -|F| |d|. Since the magnitude of force and displacement are positive, the work done is negative.
Work done is negative when the force and displacement are in opposite directions (anti-parallel).
Work done is positive when the force and displacement are in the same direction (parallel, θ=0°, cos(0°)=1). Work done is zero when the force is perpendicular to the displacement (θ=90°, cos(90°)=0).
Exit mobile version