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Question
A body of mass 70 kg, when completely immersed in water, displaces 20,000 cm3 of water. Find: (i) The weight of body in water and (ii) The relative density of material of the body.
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Solution
Weight of body = 70 kg
Volume of water displaced by body = 20,000 cm3 = 0.02 m3
(i) Mass of solid immersed in water = mass of water displaced
Mass of solid immersed in water = Density of water × Volume of water displaced
Mass of solid immersed in water = 1000 × 0.02 = 20 kg
Weight of the body, W=mg
Weight of the body in water =(70×9.8)−(20×9.8)=50 kgf
(ii) R.D. of solid = Density in C.G.S. (without unit)
Density in C.G.S. = `"mass"/"volume" = (70 xx 1000)/(20,000) = 3.5` gcm3
R.D. = 3.5
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