Physics - Rotation Question with Solution | TestHub

PhysicsRotationCalculation of M.I.Easy2 minPYQ_2020
PhysicsEasysingle choice

A nonuniform rod  OM  of length l has linear mass density that varies with the distance x from left end of the rod according to  λ= λ 0 x 3 L 3 ; Where  λ 0  is constant, is kept along x-axis and is rotating about an axis  AB , which is perpendicular to the rod as shown in the figure. What is the value of x  so that moment of inertia of rod about axis  AB  I AB  is minimum?

 

Options:

Answer:
D
Solution:

IAB=∫y2dm=λ0ℓ3∫-xl-x(y+x)3y2dy

∫(y+x)3y2dy=y2(y+x)44-∫12y(y+x)4dy

=y2(y+x)24-y10(y+x)5+110(y+x)5dy

=y2(y+x)24-y(y+x)510+(y+x)260

∫-x0(-xy2(y+x)3dx=(ℓ-x)2(ℓ)44-(ℓ-x)ℓ510+ℓ660

IAB=λ0(ℓ-x)24ℓ-110(ℓ-x)ℓ2+160ℓ3

=λ0ℓ(ℓ-x)24ℓ-110(ℓ-x)+160ℓ2

dlABdx=0⇒-(ℓ-x)2+ℓ10=0

⇒5x=4ℓ⇒x=4l5

Subject:PhysicsTopic:RotationSubtopic:Calculation of M.I.
⏱ 2mℹ️ Source: PYQ_2020

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