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NEET 2013 · Torque, Couple & Equilibrium of Rigid Bodies

Torque, Couple & Equilibrium of Rigid Bodies question from NEET 2013

Q42NEET 2013Medium

Torque, Couple & Equilibrium of Rigid Bodies

A rod PQ of mass M and length L is hinged at end P. The rod is kept horizontal by a massless string tied to point Q as shown in figure. When string is cut, the initial angular acceleration of the rod is

Figure

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Answer: (c)

  1. After the string is cut, only gravity gives torque about the hinge P: τ=MgL2\tau = Mg\frac{L}{2}.
  2. IP=ML23I_P = \frac{ML^2}{3}
  3. α=τIP=MgL/2ML2/3=3g2L\alpha = \frac{\tau}{I_P} = \frac{MgL/2}{ML^2/3} = \frac{3g}{2L}
  4. So the answer is (c).
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