question_answer

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)  0.8g/cc                                

B)  2.8g/cc

C)  1.8g/cc                

D)         0.28 g/cc

Correct Answer: B

Solution :

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\[=V\sigma \] \[ie\],\[390+250=V\times 1\,\,(as\,\,\sigma =1g/cc)\] \[ie\], 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                 \[\rho =\frac{m}{V}=\frac{390}{140}=2.8\,\,g/cc\]