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Question

A uniform rod A B of length l and mass m is free to rotate about point A. The rod is released from rest in the horizontal position. Given that the moment of inertia of the rod about A isfraction numerator m l to the power of 2 end exponent over denominator 3 end fraction, the initial angular acceleration of the rod will be

  1. fraction numerator 2 g over denominator 3 l end fraction    
  2. m g fraction numerator l over denominator 2 end fraction    
  3. fraction numerator 3 over denominator 2 end fraction g l    
  4. fraction numerator 3 g over denominator 2 l end fraction    

The correct answer is: fraction numerator 3 g over denominator 2 l end fraction


    The moment of inertia of the uniform rod about an axis through one end and perpendicular to its length is
    I equals fraction numerator m l to the power of 2 end exponent over denominator 3 end fraction
    Where m is mass of rod and l is length.
    Torque left parenthesis tau equals I alpha right parenthesis acting on centre of gravity of rod is given by
    tau equals m g fraction numerator 1 over denominator 2 end fraction
    or I alpha equals m g fraction numerator 1 over denominator 2 end fraction
    or fraction numerator m l to the power of 2 end exponent over denominator 3 end fraction alpha equals m g fraction numerator 1 over denominator 2 end fraction
    or alpha equals fraction numerator 3 g over denominator 2 l end fraction

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