Exam-style question
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Which statement best explains why a figure skater can spin faster when pulling in their arms?.
- A.Their moment of inertia increases, so torque increases.
- B.Their moment of inertia decreases, so angular momentum is conserved.
- C.Their torque increases because the force is applied closer to the axis.
- D.Their angular acceleration increases because the radius of rotation increases.
Model answer
What a good answer should say
- Their moment of inertia decreases, so angular momentum is conserved.
Explanation
Why this works
Pulling in the arms reduces the distance of mass from the axis, lowering the moment of inertia. With no external torque, angular momentum (Iω) remains constant, so a smaller I requires a larger ω, making the skater spin faster.
Common mistake
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