A cube (density 0.5 gm/cc) of side 10 cm is floating in water kept in a cylindrical beaker of base area $1500 c{m}^2$. When a mass m is kept on wooden block the level of water rises in the beaker by 2 mm. Find the mass m (in gm)

Let the cube dips further by y cm and water level rises by 2 mm

Then equating the volumes 

$\Rightarrow$ Volume of water raised = volume of extra depth of wood

$\Rightarrow 100\mathrm{y}=(1500-100)\frac{2}{10}=1400\times \frac{2}{10}=280$

$\therefore \mathrm{y}=2.8\mathrm{cm}$

$\therefore \text{ Extra upthrust }$

$\Rightarrow {\rho }_{\text{water }}\times (2.8+0.2)\times 100\mathrm{g}=\mathrm{mg}$

$\mathrm{m}=300\mathrm{gm}$