Mechanics of propulsion: A fan mounted on a stationary sailboat blows air onto its own sail — what happens? Assume still air and no external wind; the fan and sail are rigidly attached to the same boat (closed system). Choose the correct option.
IIT JEE
Physics
Difficulty: Medium
Choose an option
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AThe boat accelerates forward strongly
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BThe boat accelerates backward
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CThe boat remains essentially at rest (internal forces cancel; only small losses)
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DThe boat spins in place
Answer
Correct Answer: The boat remains essentially at rest (internal forces cancel; only small losses)
Explanation
ConceptNewton's third law and momentum conservation: fan pushes air forward; air pushes sail back ⇒ internal action–reaction cancel within the boat–air (confined) system. Net external force ≈ 0 in still air.
NotesReal effects (leaks, drag to ambient) are tiny; ideal conclusion: no net motion.
Final AnswerThe boat remains essentially at rest (internal forces cancel; only small losses)