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JEE Advanced 2016 Paper 2
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© examsnet.com
Question : 11
Total: 54
Two thin circular discs of mass m and 4m, having radii of a and 2a, respectively, are rigidly fixed by a massless, right rod of length
l
=
√
24
a
throught their center. This assembly is laid on a firm and flat surface, and set rolling without slipping on the surface so that the angular speed about the axis of the rod is
ω
. The angular momentum of the entire assembly about the point 'O' is
→
L
L (see the figure). Which of the following statement(s) is(are) true ?
The magnitude of angular momentum of the assembly about its center of mass is
17
m
a
2
ω
2
The magnitude of the z-component of
→
L
is
55
m
a
2
ω
The magnitude of angular momentum of center of mass of the assembly about the point O is
81
m
a
2
ω
The center of mass of the assembly rotates about the z-axis with an angular speed of
ω
5
Validate
Solution:
L
C
=
I
C
ω
=
1
2
m
a
2
ω
+
1
2
×
4
×
(
2
a
)
2
ω
=
17
m
a
2
ω
2
V
C
=
m
×
ω
a
+
4
m
×
2
ω
a
5
m
=
9
ω
a
5
r
⊥
=
m
l
+
4
m
×
2
l
5
m
=
9
l
5
L of cm
=
5
m
×
9
ω
a
5
×
9
l
5
=
81
m
ω
a
2
×
√
24
5
L
z
=
81
ω
a
2
√
24
5
×
c
o
s
θ
−
I
C
ω
s
i
n
θ
=
81
m
ω
a
2
×
√
24
5
×
√
24
5
−
17
m
a
2
ω
10
=
m
ω
a
2
4
[
81
×
24
5
−
17
2
]
=
1134
50
m
ω
a
2
ω
′
x
=
ω
r
ω
′
=
ω
r
x
=
ω
s
i
n
θ
ω
5
© examsnet.com
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