alleryIf the net external torque on a system is zero, then:
ALinear momentum is conserved
BMechanical energy is conserved
CKinetic energy is conserved
DAngular momentum is conserved
Answer & Solution
Correct answer: D. Angular momentum is conserved
1. dL/dt = τ_ext. If τ_ext = 0, then L is constant — conservation of angular momentum.
2. Linear momentum conservation needs zero EXTERNAL FORCE (different condition).
3. A spinning ice skater pulling arms in conserves L while KE changes — so KE is NOT conserved in general.
_Source: syllabus Physics Ch 6 §6.10 Conservation of Angular Momentum_
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