Q65 / 90 · JEE Main 2011 · Physics

A thin horizontal circular disc is rotating about a vertical axis passing through its centre. An insect is at rest at a point near the rim of the disc. The insect now moves along a diameter of the disc to reach its other end. During the journey of the insect, the angular speed of the disc:

  • A
    continuously decreases
  • B
    continuously increases
  • Correct answer
    C
    first increases and then decreases
  • D
    remains unchanged

Solution

$$ \tau=0 $$ Angular momentum is conserve $$ \mathrm{I}_1 \omega_1=\mathrm{I}_2 \omega_2 \Rightarrow \omega_2=\frac{\mathrm{I}_1 \omega_1}{\mathrm{I}_2} $$ $\mathrm{I}_2$ first decreases and then increases $\therefore \omega$ first increases and then decreases.

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

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