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.
Mechanical Engineering
Engineering Mechanics
Difficulty: Easy
Choose an option
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ASome force acts on a body, but displacement is zero
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BNo force acts on a body but some displacement takes place
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CEither (a) or (b)
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DNone of the above
Answer
Correct Answer: Either (a) or (b)
Explanation
ConceptWork 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 AnswerEither (a) or (b)