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Concepts Of Physics MCQ Edition [Volume 1]PhysicsRotational Mechanics

A boy sits in a revolving chair that rotates at an angular speed of 120 revolutions per minute. Two heavy balls are part of the revolving system, and the boy can pull the balls closer to himself or push them apart. If the boy decreases the moment of inertia of the system from 6 kg-m ^2 to 2 kg-m ^2 by pulling the balls closer, determine the new angular speed.

Options

  1. A180 revolutions per minute
  2. B40 revolutions per minute
  3. C240 revolutions per minute
  4. D360 revolutions per minute

Correct answer

D. 360 revolutions per minute

Step-by-step solution

According to the principle of conservation of angular momentum, if no external torque acts on a system, its total angular momentum remains constant. I₁ ₁ = I₂ ₂ Given: I₁ = 6 kg-m ^2 ₁ = 120 rpm I₂ = 2 kg-m ^2 Substituting the values into the equation: 6 120 = 2 ₂ ₂ = 6 120 2 ₂ = 360 rpm

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