A thin circular plate of mass M and radius R has its density varying as ρ ( r ) =ρ 0 r with ρ 0 as constant…

A thin circular plate of mass M and radius R has its density varying as ρ(r)0r with ρ0 as constant and r is the distance from its centre. The moment of Inertia of the circular plate about an axis perpendicular to the plate and passing through its edge is I=aMR2. The value of the coefficient a is:
  1.  35
  2.  12
  3.  85
  4.  32

Solution

dm=2πrdr×ρ=2πρ0r2dr
M=2πρ00Rr2dr=23πρ0R3
ICM=ρdmr2=2πρ0r4dr=25πρ0R5
Icm=35MR2
I=Icm+MR2=85MR2

Asked in: JEE Main 2019 (08 Apr Shift 1)

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