A glass flask weighing 390 g having internal volume 500 cc just floats

A glass flask weighing 390 g having internal volume 500 cc just floats when half of it is filled with water. Specific gravity of the glass is

(a) 2.8
(b) 1.8
(c) 1
(d) 2.5

2.8

Weight of the flask + 250 c.c. of water is balanced by V₂ gm of water.

Where V₂ is the external volume.

.·. (390 + 250)g = V₂ × 1 × g ⇒ V₂ = 640 c.c.

.·. Volume of the material = (640 – 500) c.c. = 140 c.c.

.·. Density of glass = 390 g / 140 c.c. = 2.8 g/c.c.

i.e. Specific gravity = 2.8

OA2007

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