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.

Difficulty: Medium

The boat accelerates forward strongly
The boat accelerates backward
The boat remains essentially at rest (internal forces cancel; only small losses)
The boat spins in place

Correct Answer: The boat remains essentially at rest (internal forces cancel; only small losses)

Explanation:

Concept
Newton'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.

Notes
Real effects (leaks, drag to ambient) are tiny; ideal conclusion: no net motion.

Final Answer
The boat remains essentially at rest (internal forces cancel; only small losses)

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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.

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