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MHT CET202521 Apr 2025Morning ShiftPhysicsRotational MotionActual

A disc of mass 25 kg and radius 0.2 m is rotating at 240 r.p.m. A retarding torque brings it to rest in 20 second. If the torque is due to a force applied tangentially on the rim of the disc then the magnitude of the force is

Options

  1. A2 ~N
  2. B2 ~N
  3. CN
  4. D4 ~N

Correct answer

C. N

Step-by-step solution

The initial angular speed is ₀ = 240 2 60 = 8 rad/s , and the disc comes to rest so = 0 . Using = ₀ + t with t = 20 s gives 0 = 8 + 20 , leading to = - 2 5 rad/s ^2 , with magnitude | | = 2 5 rad/s ^2 . The moment of inertia is I = 1 2 MR^2 = 1 2 (25)(0.2)^2 = 0.5 kg m ^2 . The torque is = I| | = 0.5 2 5 = 5 N m . Since = FR , the force magnitude is F = /5 0.2 = N .

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