The work done by a force is considered zero if either the displacement of the object is zero or the force acts perpendicular to the direction of displacement. In mathematical terms, W = F⋅ s ⋅ cos(θ), where θ is the angle between the force and displacement vectors. When θ=90° cos (90°) =0, hence W = 0.
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The work done by a force is considered zero when either the force applied is zero, the displacement of the object is zero, or the force is perpendicular to the direction of displacement. In these cases, there is no component of the force in the direction of the displacement.