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An ornament weighs 36 g in air and only 34 g when fully immersed in water. It is made of gold mixed with some copper. Find the mass of copper present. Specific gravity of gold = 19.3, of copper = 8.9.
- 1.4 gm
- 1.8 gm
- 2.1 gm
- 2.2 gm
Correct answer: 2.2 gm
Solution
The apparent loss of weight in water (36 - 34 = 2 g) equals the mass of water displaced, so the total volume of the ornament is 2 cc. Let m be the copper mass; gold mass is (36 - m). Volume = (36 - m)/19.3 + m/8.9 = 2. Solving: 8.9(36 - m) + 19.3 m = 2 * 19.3 * 8.9. That gives 320.4 - 8.9m + 19.3m = 343.54, so 10.4 m = 23.14, m = 2.22 g, approximately 2.2 g.
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