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JEE Main 2007
Exam
JEE Main
Year
2007
Subject
Physics
Chapter
Center of Mass, Momentum and Collision

JEE Main 2007 · Physics · Center of Mass, Momentum and Collision

A circular disc of radius R is removed from a bigger circular disc...

A circular disc of radius R\mathrm{R} is removed from a bigger circular disc of radius 2R\mathrm{2R} such that the circumferences of the discs coincide. The centre of mass of the new disc is α/R\mathrm{\alpha / R} from the centre of the bigger disc. The value of α\mathrm{\alpha} is

Options

  1. A1/31 / 3
  2. B1/21 / 2
  3. C1/61 / 6
  4. D1/41 / 4

Correct answer

A. 1/31 / 3

Step-by-step solution

In this question distance of centre of mass of new disc is αR\alpha R not αR\frac{\alpha}{R}. −3M4αR+M4R=0⇒α=13\begin{aligned} & -\frac{3 \mathrm{M}}{4} \alpha \mathrm{R}+\frac{\mathrm{M}}{4} \mathrm{R}=0 \\ & \Rightarrow \alpha=\frac{1}{3} \end{aligned}
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