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JEE Main 25 July 2021 Shift 1 Solved Paper
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© examsnet.com
Question : 2
Total: 90
Given below are two statements: one is labelled as
Assertion
A
and the other is labelled as
Reason
R
.
Assertion A:
Moment of inertia of a circular disc of mass '
M
' and radius 'R' about
X
,
Y
axes (passing through its plane) and Z-axis which is perpendicular to its plane were found to be
I
x
,
I
y
and
I
z
respectively. The respective radii of gyration about all the three axes will be the same.
Reason R :
A rigid body making rotational motion has fixed mass and shape. In the light of the above statements, choose the most appropriate answer from the options given below:
[25 Jul 2021 Shift 1]
Both A and R are correct but R is NOT the correct explanation of A.
A is not correct but R is correct.
A is correct but R is not correct.
Both A and R are correct and R is the correct explanation of A.
Validate
Solution:
I
z
=
I
x
+
I
y
(using perpendicular axis theorem)
&
I
=
m
k
2
(
K
:
radius of gyration
)
so
m
K
z
2
=
m
K
x
2
+
m
K
y
2
K
z
2
=
K
x
2
+
K
y
2
so radius of gyration about axes
x
,
y
&
z
won't be same hense asseration
A
is not correct reason
R
is correct statement (property of a rigid body)
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