A wooden cube floating in water supports a mass $m=0.2kg$ at its top. When the mass is removed the cube rises by $2cm$. the side of cube is ___ cm.
(density of water $1000kg/m^3$  )
 

Decrease in weight = decrease in upthrust
or    $mg=V{\rho }_{w}g$        
or    $m=V{\rho }_w$        
or  $\left(0.2\right)=(2\times {10}^{-2})\left(A\right)\left({10}^3\right)(A=areaofbase)$           
or   $A={10}^{-2}{m}^2=100c{m}^2$         
  Side of the cube is $10cm$ .