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NEET PHYSICSMedium

A thin rod of length LL and mass MM is bent at its midpoint into two halves so that the angle between them is 9090^{\circ}. The moment of inertia of the bent rod about an axis passing through the bending point and perpendicular to the plane defined by the two halves of the rod is:

A

ML224\frac{ML^2}{24}

B

ML212\frac{ML^2}{12}

C

ML26\frac{ML^2}{6}

D

2ML224\frac{\sqrt{2}ML^2}{24}

Step-by-Step Solution

Let the total mass of the rod be MM and its total length be LL. When it is bent at its midpoint, it forms two halves, each of mass m=M2m = \frac{M}{2} and length l=L2l = \frac{L}{2}. The axis passes through the bending point (which is one end of each half) and is perpendicular to the plane containing both halves. For a uniform rod of mass mm and length ll, the moment of inertia about an axis passing through its end and perpendicular to its length is given by I=ml23I = \frac{ml^2}{3}. The moment of inertia of each half about the given axis is: I1=I2=13ml2=13(M2)(L2)2=13×M2×L24=ML224I_1 = I_2 = \frac{1}{3} m l^2 = \frac{1}{3} \left(\frac{M}{2}\right) \left(\frac{L}{2}\right)^2 = \frac{1}{3} \times \frac{M}{2} \times \frac{L^2}{4} = \frac{ML^2}{24} The total moment of inertia is the scalar sum of the moments of inertia of both halves: Itotal=I1+I2=ML224+ML224=2ML224=ML212I_{total} = I_1 + I_2 = \frac{ML^2}{24} + \frac{ML^2}{24} = \frac{2ML^2}{24} = \frac{ML^2}{12}

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