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JEE Main20199 Jan 2019Morning ShiftPhysicsRotational MotionActual

Two masses m and m 2 are connected at the two ends of a massless rigid rod of length l . The rod is suspended by a thin wire of torsional constant k at the centre of mass of the rod-mass system (see figure). Because of torsional constant k , the restoring torque is τ = k θ for angular displacement θ . If the rod is rotated by θ 0 and released, the tension in it when it passes through its mean posi

Options

  1. Ak θ 0 2
  2. B3 k θ 0 2 l
  3. C2 k θ 0 2 l
  4. Dk θ 0 2 l

Correct answer

D. k θ 0 2 l

Step-by-step solution

When rod is rotated by angle α , the twist in the wire is ϕ . angular frequency of wire, Ω = k I angular frequency of rod, ω = θ 0 . Ω Max. Tension in the rod = m ω 2 . l 3 = m θ 0 2 . k I . l 3 , here I = m l 2 3 = θ 0 2 k l

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