A Wooden Stick Of Length L, Radius R and Density  has A Small Metal Piece Of Mass m (of Negligible Volume) Attached To Its One End. Find The Minimum Value Of The Mass m (in Terms Of Given Parameters) That Would Make The Stick Float Vertically In Equilibrium In A Liquid Of Density . 

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Question

A wooden stick of length L, radius R and density  has a small metal piece of mass m (of negligible volume) attached to its one end. Find the minimum value of the mass m (in terms of given parameters) that would make the stick float vertically in equilibrium in a liquid of density 

Solution

Correct option is

 

For the stick to be vertical for rotational equilibrium, centre of gravity should be below in a vertical line through the centre of buoyancy. For minimum m, the two will coincide. 

Let h be the length of immersed portion. For translatory equilibrium, 

   Wt. of rod + mass attached = force of buoyancy  

              

  

The height of centre of mass from bottom 

          

       

For rotator equilibrium and for minimum m, this should be equal to h/2. 

   

   

Substituting for h in eq. (i), we get 

       

       

         

       

            

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