alleryStart learning →Under what condition is the angular momentum of a system conserved?
AWhen its rotational kinetic energy is constant
BWhen the net external torque on it is zero
CWhen the net external force on it is zero
DWhen its moment of inertia stays constant
Answer & Solution
Correct answer: B. When the net external torque on it is zero
1. Torque and angular momentum are linked by net tau = delta L / delta t.
2. If the net external torque is zero, then delta L / delta t is zero.
3. A quantity with zero rate of change is constant, so L = L prime.
4. Zero net force conserves linear momentum instead, which is a separate statement.
5. A spinning skater changes her moment of inertia yet still conserves angular momentum, so constant I is not the condition.
_Source: OpenStax College Physics (CC BY 4.0), Ch 10 "Rotational Motion and Angular Momentum", section 10.5 Angular Momentum and Its Conservation_
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