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The principle of conservation of linear momentum holds for a system of bodies only when
AAll the bodies have an equal mass
BNo net external force acts on the system
CThe bodies move at a constant speed
DAn external force acts continuously
Answer & Solution
Correct answer: B. No net external force acts on the system
1. The principle states total momentum stays constant if no net external force acts.
2. Internal action-reaction forces cancel out by Newton's third law.
3. So conservation needs the net external force to be zero.
4. Rule out option D: an external force would change the total momentum.
_Source: Samacheer Kalvi (TN SCERT) Class 10 Science, Unit 1 "Laws of Motion", p.14_
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