Q31 / 122 · NTA Abhyas (JEE Main) 2020 · Physics · Rotational Motion

A thin circular plate of mass M and radius R has its density varying as ρ(r)=ρ0r 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:

  • A
     35
  • B
     12
  • Correct answer
    C
     85
  • D
     32

Solution

dm=2πrdr×ρ=2πρ0r2dr
M=2πρ0∫0Rr2dr=23πρ0R3
I=ρdmr2=2πρ0∫r4dr=25πρ0R5
Icm=35MR2
I=Icm+MR2=85MR2

Hence, the correct answer is option: 'C'.

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