Direction for: In each of the following questions a statement of Assertion is given followed by a corresponding statement of Reason just below it. Of the statements mark the correct answer as
Assertion: For system of particles under central force field, the total angular momentum is conserved. Reason: The torque acting on such a system is zero.A) If both assertion and reason are true and reason is the correct explanation of assertion.
B) If both assertion and reason are true but reason is not the correct explanation of assertion.
C) If assertion is true but reason is false.
D) If both assertion and reason are false.
Correct Answer: A
Solution :
Key Idea: Torque is rate of charge of angular momentum of a body. When a body rotates about an axis under the action of an external torque t, then the rate of change of angular momentum of the body is equal to the torque, that is \[\frac{dJ}{dt}=\tau \] If external torque is zero \[(\tau =0)\], then \[\frac{dJ}{dt}=0\] \[\Rightarrow \] \[dJ=0\] \[\Rightarrow \] J= constant Thus, angular momentum remains conserved.
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