Q41 / 105 · NTA Abhyas (JEE Main) 2020 · Physics · Center of Mass Momentum and Collision

There is a thin uniform disc of radius R and mass per unit area σ, in which a hole of radius R/2 has been cut out as shown in the figure. Inside the hole, a square plate of same mass per unit area σ is inserted so that its corners touch the periphery of the hole. The distance of the centre of mass of the system from the origin is

Figure

  • Correct answer
    A
    R(2-π)23π+2
  • B
    R(1-π)22π+1
  • C
    2 R π 2 3 π + 2
  • D
    3 R π 2 2 π + 1

Solution

Side of square = R cos 4 5 ∘ = R 2

Area of square = R 2 2

XCOM=π×R2×σ×0+π×R24-σ×R2+R22×σ×R2π×R2×σ+π×R24-σ+R22×σ

=R(2-π)2(3π+2)

∴  The centre of mass of the system is at a distance of R(2-π)2(3π+2) from the centre O towards the plate as shown in the figure

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

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