A stick of square cross-section  $(5cm\times 5cm)$ and length ‘4 m’ weighs 2.5 kg is in equilibrium as shown in the figure below. Determine its angle of inclination (in degree) in equilibrium when the water surface is 1 m above the hinge.    

  $OE=l$
  $l=\frac{1}{\sin \theta } \mathrm{...........}\left(i\right)$
$OD=2\cos \theta \mathrm{............}\left(ii\right)$  
$OC=\frac{l}{2}\cos \theta =\frac{\cos \theta }{2\sin \theta } \mathrm{..........}\left(iii\right)$  
$F_B={\rho }_{w}Alg$  
Torque about  $O$
                                  $mg\left(OD\right)={\rho }_{w}Alg\left(OC\right)$
On solving 
          ${\sin }^2\theta =\frac{1}{4}$
          $\theta ={30}^0$