Question

A wooden block floating in a bucket of water has $\frac{4}{5}$ of its volume submerged. When certain amount of an oil is poured into the bucket, it is found that the block is just under the oil surface with half of its volume under water and half in oil. The density of oil relative to that of water is?

• A. $0.5$
• B. $0.7$
• C. $0.6$
• D. $0.8$

Answer 1

The correct option is C $0.6$

In $1^{st}$ situation
$V_b{\rho }_{b}g=V_s{\rho }_{w}g$

$\frac{V_s}{V_b}=\frac{{\rho }_b}{{\rho }_w}=\frac{4}{5}$ ...(i)

here

$V_b$ is volume of block
$V_s$ is submerged volume of block
${\rho }_b$ is density of block
${\rho }_w$ is density of water
& Let ${\rho }_o$ is the density of oil

finally in equilibrium condition
$V_b{\rho }_{b}g=\frac{V_b}{2}{\rho }_{o}g+\frac{V_b}{2}{\rho }_{w}g$
$2{\rho }_b={\rho }_o+{\rho }_w$
$\Rightarrow \frac{{\rho }_o}{{\rho }_w}=\frac{3}{5}=0.6$.