An ornament weighting 36g in air, weighs only 34g in water. Assuming that some copper is mixed with gold….

Q: An ornament weighting 36g in air, weighs only 34g in water. Assuming that some copper is mixed with gold to prepare the ornament, find the amount of copper in it. Specific gravity of gold is 19.3 and that of copper is 8.9 .

(a) 2.2 g

(b) 2.4 g

(c) 4.2 g

(d) 5.2 g

Ans: (a)

Sol: Loss of weight in water = 36 – 34 = 2 g

V ρw g = 2 g

V = 2 cm3

Let m = mass of copper , (36-m ) = mass of gold

$\large V = V_G + V_C$

$\large 2 = \frac{36-m}{19.3} + \frac{m}{8.9} $

m = 2.2 g

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