Rotation 1 Question 18

21. The moment of inertia of a thin square plate ABCD, of uniform thickness about an axis passing through the centre O and perpendicular to the plane of the plate is

(1992,2M)

(a) I1+I2

(b) I3+I4

(c) I1+I3

(d) I1+I2+I3+I4

where, I1,I2,I3 and I4 are respectively moments of inertia about axes 1, 2, 3 and 4 which are in the plane of the plate.

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Answer:

Correct Answer: 21. (a, b, c)

Solution:

  1. Since, it is a square lamina

I3=I4 and I1=I2

(by symmetry)

From perpendicular axes theorem,

Moment of inertia about an axis perpendicular to square plate and passing from O is

or

Io=I1+I2=I3+I4

 Hence, I2=I3

Rather we can say I1=I2=I3=I4

Therefore, Io can be obtained by adding any two i.e.

Io=I1+I2=I1+I3=I1+I4=I2+I3=I2+I4=I3+I4



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