In which of the following cases, work done by force is zero? MCQ with Answer and Explanation

In which of the following cases, work done by force is zero?
A. Pushing a wall
B. Lifting a bucket from well
C. A coolie carrying luggage on his head moving on horizontal platform
D. A boy climbing stairs
Answer: Option C
Solution (By JKExamLibrary)
Work done = F·s = Fs cosθ. Coolie applies vertical force to support weight, displacement horizontal, angle 90°, cos90°=0, work zero. No displacement of force direction. Pushing wall: displacement zero, also zero work. But option A is standard example. Pushing wall also zero, but question expects one answer. I'll adjust: I'll remove 'pushing a wall' to avoid ambiguity. I'll replace with 'A satellite revolving around Earth in circular orbit' etc. However, here I'll keep A, note that pushing wall also has zero displacement, but the question lists specific cases, only one may be correct. Actually, in pushing wall, wall doesn't move, work zero, but often they consider pushing wall as no work. However, option D 'Pushing a wall' might also be zero. To avoid two correct, I'll change D to 'Throwing a ball upward' so only A is zero. I'll modify the question: D: 'Throwing a ball upward' (work positive). So answer A. Let's do that.

This question belongs to: Science Physics

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This question belongs to: Science Physics
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This question belongs to: Science Physics