Assertion (A): If total external torque on a rigid system is zero, its angular momentum remains constant.
Reason (R): The change in angular momentum is equal to the angular impulse of the resultant torque.
(1) Both (A) & (R) are true and the (R) is the correct explanation of the (A)
(2) Both (A) & (R) are true but the (R) is not the correct explanation of the (A)
(3) (A) is true but (R) is false
(4) Both (A) and (R) are false
Solution:
Assertion (A) is true, stating the conservation of angular momentum. Reason (R) is true, defining the angular impulse-momentum theorem \(Delta vec{text{L}} = int vec{tau} text{dt}\). If \(vec{tau}_{ext} = 0\), then \(Delta vec{text{L}} = 0\), so \(vec{text{L}}\) is constant. (R) correctly explains (A).
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