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⚛️ Physics  ·  System of Particles and Rotational Motion  ·  NEET & JEE

A horizontal disk rotating at ω has a coefficient of friction μ between it and a small block placed at distance r from centre. The block will start sliding if:

Answer: ω > √(μg/r).

  • A ω > √(μg/r)
  • B ω < √(μg/r)
  • C ω = μg/r
  • D ω > μgr

Correct answer: A. ω > √(μg/r)

Explanation: Static friction provides centripetal force: μmg ≥ mω²r. Sliding occurs when ω²r > μg, i.e., ω > √(μg/r).

axis OPr⊥Fττ = r⊥ × F = r × F × sinθ

Torque about axis O equals the force F multiplied by the perpendicular distance r⊥ from the axis to the line of action of the force, producing rotation.

Concept context

Moment of inertia, torque, angular momentum, rolling motion. Very high JEE weightage.

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