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Work and energy — when is work done equal to zero? Assess the given conditions and determine under which situation(s) the mechanical work done is zero. Choose the correct option.

Difficulty: Easy

Some force acts on a body, but displacement is zero
No force acts on a body but some displacement takes place
Either (a) or (b)
None of the above

Correct Answer: Either (a) or (b)

Explanation:

Concept
Work done W = 𝐹 ⃗ ⋅ 𝑠 ⃗ = 𝐹 𝑠 cos ⁡ 𝜃 F ⋅ s =Fscosθ. Work is zero if either the force is zero or the displacement is zero (or if the force is perpendicular to the displacement, θ = 90°).

Assessment of options

(a) s = 0 → W = 0.
(b) F = 0 → W = 0.
Therefore, either (a) or (b) implies zero work.

Final Answer
Either (a) or (b)

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