Question

A block of wood flots in water with $\frac{4}{5}$th of its volume submerged, but it just floats in another liquid. The density of liquid is (in kg/$m^3$)

• A. 750
• B. 800
• C. 1000
• D. 1250

Answer 1

The correct option is B 800

Let V be the volume of the block.

When float in water :

$v{\rho }_{b}g=\frac{4}{5}v{\rho }_{w}g$

${\rho }_{block}=\frac{4}{5}{\rho }_w$

and ${\rho }_w=1000kg/m^3$

so ${\rho }_b=\frac{4}{5}\times 1000=800kg/m^3$

Hence option B is correct.