Question

A glass flask having mass $390\text{g}$ and an interior volume of $500{\text{cm}}^3$ floats completely inside water, when it is half filled with water. The density of the material of the flask is

• A. $0.8\text{g/cc}$
• B. $2.8\text{g/cc}$
• C. $1.8\text{g/cc}$
• D. $0.8\text{g/cc}$

Answer 1

The correct option is B $2.8\text{g/cc}$

According to Archimedes' principle,
$m_{g}g+m_{w}g=F_B$
$390\times g+250\times {\rho }_w\times g=v{\rho }_{w}g$
Using ${\rho }_w=1\text{g/cc},$ we get $v=640{\text{cm}}^3$
Volume of glass $=640-500=140{\text{cm}}^3$
Density of material of flask $\rho =\frac{390}{140}$
$=2.8\text{g/cc}$