Question

12) Assertion (A) – Ballet dancer, while performing, folds her arms to spin faster.
Reason (R) – By folding arms, ballet dancer decreases the moment of inertia and increases the angular velocity keeping angular momentum constant.
a) Both A and R are true and R is correct explanation of A
b) Both A and R are true and R is not correct explanation of A
c) A is true R is false
d) A is false and R is also false

Answer 1

Answer:

a) Both A and R are true and R is correct explanation of A

Explanation:

• folding and opening of arms is totally a internal force as only normal forces are acting on it.
• so no external force are present..then momentum will remain constant or conserved
• no external force...no external torque, angular momentum will also remains constant.
• as angular momentum (Ĺ) = Iw (w is omega or angular velocityl
• so as she closes the are its inertia decreases (as its directly proportional to distance from axis) so to counter the effect of it onega increases
• by which Ĺ remains conserved.

hope it helps!