Question

A glass flask having mass $390\, g$ and an interior volume of $ 500\,c{{m}^{3}} $ floats on water when it is less than half filled with water. The density of material of the flask is

• A. 0.8 g/cc
• B. 2.8 g/cc
• C. 1.8 g/cc
• D. 0.28 g/cc

Answer 1

Answer: (B)

As the flask floats in water when less than half filled with water, it will float just fully submerged when half filled.
In this situation, mass of flask + mass of water in it
$=V \sigma i e, 390+250=V \times 1(as \sigma=1\, g / c c)$

i.e, outer volume of flask
$V=640 \,cc$
Now as inner volume of flask is given to be $500 \,cc$, so the volume of the material of flask $=640-500=140 \,cc .$
But as mass of flask is $390 \,g$, so density of material of flask
$\rho=\frac{m}{V}=\frac{390}{140}=2.8 \,g/cc $