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The source calls a system isolated when a specific condition holds. What is that condition?
AThe system has no internal forces at all
BThe system contains only a single object
CThe net external force on the system is zero
DThe system's total mass never changes
Answer & Solution
Correct answer: C. The net external force on the system is zero
1. The source defines this term specifically in the context of momentum conservation.
2. An isolated system is one for which the net external force is zero.
3. Such a system can still contain several objects that exert forces on each other internally.
4. Nothing in this definition requires the system's total mass to stay fixed, only that no outside net force acts on it.
_Source: OpenStax College Physics (CC BY 4.0), Ch 8 "Linear Momentum and Collisions", section 8.3 Conservation of Momentum_
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