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A porter carries a $20$ kg bag horizontally for $50$ m at constant height. The work done by him on the bag against gravity is:
A$1000$ J, since $W = mgh$ with $h = 50$ m considered
B$500$ J, half the simple weight-distance product value
CZero, since displacement is perpendicular to gravity here
D$10000$ J, the bag mass times the long ground path
Answer & Solution
Correct answer: C. Zero, since displacement is perpendicular to gravity here
Gravity acts vertically; displacement is horizontal; $\cos 90^\circ = 0$, so work against gravity is zero.
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