Mechanical Properties of Solids

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Question : 13
Total: 21
What is the density of water at a depth where pressure is 80.0 atm, given that its density at the surface is 1.03×103 kg m3? Compressibility of water is 45.8×1011Pa1.
Solution:  
Here, P=80.0atm.
=80.0×1.013×105Pa
Compressibility,
1
B
=45.8×1011Pa1

Density of water at surface, ρ=1.03×103kgm3
Let ρ′ be the density of water at the given depth. If V and V′ are volume of certain mass M of ocean water at surface and at a given depth, then
V=
M
ρ
and V"=
M
ρ"

Change in volume, ΔV=VV"=M(
1
ρ
1
ρ"
)

Volumetric strain,
ΔV
V
=M(
1
ρ
1
ρ
)
×ρM
=1
ρ
ρ
or
ΔV
V
=1
1.03×103
ρ
.
.
.(i)

As, Bulk modulus B=
PV
ΔV
or
ΔV
V
=
P
B

ΔV
V
=(80.0×1.013×105)×45.8×1011
=3.712×103
Putting this value in (i) we get
1
1.30×103
ρ
=3.712×103

or ρ=
1.30×103
13.712×103

=1.034×103kgm3
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