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BITSAT 2017 Solved Question Paper
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© examsnet.com
Question : 21
Total: 150
A steel wire of length ‘L’ at 40°C is suspended from the ceiling and then a mass ‘m’ is hung from its free end. The wire is cooled down from 40°C to 30°C to regain its original length ‘L’. The coefficient of linear thermal expansion of the steel is
10
–
5
°
C
, Young’s modulus of steel is
10
11
N
/
m
2
and radius of the wire is 1 mm. Assume that L >>diameter of the wire. Then the value of ‘m’ in kg is nearly
1
2
3
5
Validate
Solution:
We know that
Y
=
m
g
A
∆
l
l
=
m
g
l
A
∆
l
...(1)
Also
∆
l
=
l
α
∆
T
.....(2)
From (1) and (2)
Y
=
m
g
l
A
l
α
∆
T
=
m
g
A
α
∆
T
∴
m
=
Y
A
α
∆
T
g
=
10
11
×
π
(
10
−
3
)
2
×
10
−
5
×
10
10
=
π
≈
3
© examsnet.com
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