A porter carries a suitcase horizontally across a platform at constant speed. The work done by the porter against gravity is
Correct answer: B. zero
- A. equal to mgh
- B. zero
- C. equal to the weight times the distance walked
- D. negative
Explanation
The upward force supporting the suitcase is perpendicular to the horizontal displacement, so the work done against gravity is zero. The porter still expends metabolic energy holding the case up, but that is not mechanical work on the suitcase, which is the standard point of this question. Work against gravity appears only when the height changes.
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About Work
Work is done when a force produces displacement, with its value determined by the component of force along the displacement. The topic covers positive, negative and zero work, work by variable forces from force-displacement graphs, and the connection between net work and change in kinetic energy.
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