Question

The conservation of angular momentum demands that

• A. the external force on the system must be zero
• B. the external torque on the system must be zero
• C. both the external force as well as the external torque must be zero
• D. neither of them must be zero

Answer 1

Answer: (B)

the external torque on the system must be zero

Answer 2

From law of conservation of angular momentum, if no external torque acts on a system, then total vector sum of angular momentum of different particles of the system remains conserved.
$\tau_{\text {ext }}=0$ then $\frac{d L}{d t}=0$