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A block of mass m is attached to one end of a light string which is wrapped on a disc of mass 2 m and radius R . The total length of the slack portion of the string is l . The block is released from rest. The angular velocity of the disc just after the string becomes taut is

Options

  1. Agl R 2
  2. Bgl 2R 2
  3. C2gl 3R 2
  4. D3gl 2R 2

Correct answer

B. gl 2R 2

Step-by-step solution

Using the principle of conservation of angular momentum, m 2 gl × R = 2 m   R 2 2 + mR 2 × ω ⇒ ω = gl 2 R 2

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