Q. A gramophone record is revolving with an angular velocity ω. A coin is placed at a distance r from the centre of the record. The static coefficient of friction is μ. The coin will revolve with the record if
A) r ≥ μg/ω²
B) r = μgω²
C) r < ω²/(μg)
D) r ≤ μg/ω²
Explanation
[Solution from source] Static friction supplies the centripetal force: mrω² ≤ μmg, so the coin stays on if r ≤ μg/ω². The reversed inequality r ≥ μg/ω² describes when the coin slips off. Answer (4).
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.