NEETPhysicsRotational Motion
Given below are two statements: one is labelled as Assertion (A) and the other is labelled as Reason (R). Assertion (A): When a person spinning on a frictionless chair pulls their arms inwards, their rotational kinetic energy increases even though no external torque acts on the system. Reason (R): When the person pulls their arms inwards, the angular momentum of the system increases, leading to an increase in rotatio
Options
- ABoth (A) and (R) are correct and (R) is the correct explanation of (A)
- BBoth (A) and (R) are correct but (R) is not the correct explanation of (A)
- C(A) is correct but (R) is not correct
- D(A) is not correct but (R) is correct
Correct answer
C. (A) is correct but (R) is not correct
Step-by-step solution
Assertion (A) is correct: When the person pulls their arms inwards, their moment of inertia ( I ) decreases. Since no external torque acts on the system, angular momentum ( L ) is conserved. The rotational kinetic energy is given by K = L^2 2I . As I decreases while L remains constant, the rotational kinetic energy K increases. The extra energy comes from the internal work done by the person's muscles. Reason (R) is incorrect: The angular momentum of the system does not increase; it remains conserved because the ne