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

A wheel of moment of inertia 2 kg·m<sup>2</sup> spinning at 50 rad/s is stopped by a constant retarding torque of 5 N·m. The time taken to stop is:

Answer: 20 s.

  • A 5 s
  • B 10 s
  • C 20 s
  • D 40 s

Correct answer: C. 20 s

Explanation: Angular retardation α = τ/I = 5/2 = 2.5 rad/s<sup>2</sup>. Time to stop = ω/α = 50/2.5 = 20 s.

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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