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A piece of wood of uniform cross-section and 15 cm height sinks 10 cm in water and 12 cm in spirit. Find the R.D. of wood and spirit.

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Question

A piece of wood of uniform cross-section and 15 cm height sinks 10 cm in water and 12 cm in spirit. Find the R.D. of wood and spirit.
Answer in Brief
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Solution

The fractional part submerged equals the ratio of the density of the material of the block to the density of the liquid.
(Density of floating body / Density of liquid) = fraction submerged.
Height of wooden piece = 15 cm.
Height of wooden piece sinks in water = 10 cm.
Fraction of wooden piece submerged in water = 10/15 = 0.67.
As the liquid is water so the ratio of Density of wooden by the density of water gives a relative density of floating wooden pieces. So, the relative density of the wooden block is 0.67.
Height of wooden piece = 15 cm.
Height of wooden piece sinks in spirit = 12 cm.
Fraction of wooden piece submerged in water = 12/15 = 0.8.
We know the density of wooden piece = 0.67
(Density of floating body / Density of liquid) = fraction submerged.
Density of liquid/spirit = (Density of floating body /fraction submerged)
Density of liquid/spirit = 0.67/0.8 = 0.83.
The relative density of the spirit is 0.83.

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Determination of Relative Density of a Solid Substance by Archimedes’ Principle
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Chapter 4: Fluids - Exercise 2 [Page 174]

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Frank Physics Part 1 [English] Class 9 ICSE
Chapter 4 Fluids
Exercise 2 | Q 23 | Page 174

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