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Test Index
JEE Main Physics Class 11 System of Particles and Rotational Motion Part 1 Questions
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© examsnet.com
Question : 14
Total: 100
Two coaxial discs, having moments of inertia
I
1
and
I
1
2
,
are rotating with respective angular velocities
ω
1
and
ω
1
2
, about their common axis. They are brought in contact with each other and thereafter they rotate with a common angular velocity. If
E
f
and
E
i
are the final and initial total energies, then
(
E
f
−
E
i
)
is:
[10 Apr. 2019 I]
−
I
1
ω
1
2
12
I
1
ω
1
2
6
3
8
I
1
ω
1
2
−
I
1
ω
1
2
24
Validate
Solution:
As no external torque is acting so angular momentum should be conserved
(
I
1
+
I
2
)
ω
=
I
1
ω
1
+
I
2
ω
2
[
ω
c
=
.
common angular velocity of the system, whendiscs are in contact]
ω
c
=
I
1
ω
1
I
1
ω
1
4
I
1
+
I
1
2
(
5
4
×
2
3
)
ω
1
ω
c
=
5
ω
1
6
E
f
−
E
i
=
1
2
(
I
1
+
I
2
)
ω
c
2
−
1
2
I
1
ω
1
2
−
1
2
I
2
ω
2
2
Put
I
2
=
I
1
∕
2
and
ω
c
=
5
ω
1
6
5
ω
1
∕
6
We get :
E
f
−
E
i
=
−
I
1
ω
1
2
24
© examsnet.com
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