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Question
A solid of R.D. 4.2 is found to weigh 0.200 kgf in air. Find its apparent weight in water.
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Solution
Relative density of solid = R.D. = 4.2
Weight of solid in air = W = 0.200 kgf
R.D. = `"Weight of solid in air"/("wt. of solid in air" - "wt. of solid in water")`
Also, wt. of solid in air - Wt. of solid in water = Upthrust
R.D. = `"Wt. of solid in air"/"Upthrust"`
`4.2 = 0.200/"Upthrust"`
Upthrust = `0.200/4.2 = 0.0476` kgf
So, apparent wt. of solid in water = wt. of solid in air - Upthrust
= 0.200 - 0.0476 = 0.1524 ≅ 0.15 kgf
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