MCQ
Three objects, $A :$ (a solid sphere), $B :$ (a thin circular disk) and $C :$ (a circular ring), each have the same mass $M$ and radius $R.$ They all spin with the same angular speed $\omega$ about their own symmetry axes. The amounts of work $(W)$ required to bring them to rest, would satisfy the relation
  • A
    $W_C>W_B>W_A$
  • B
    $W_A>W_B>W_C$
  • C
    $W_A>W_C>W_B$
  • D
    $W_B>W_A>W_C$

Answer

Work done required to bring a object to rest $\Delta W=\Delta K E$
$\Delta W=\frac{1}{2} I \omega^2 ;$ where $I=$ moment of inertia
For same $\omega, \Delta W \propto I$
For a solid sphere, $I_A=\frac{2}{5} M R^2$
For a thin cicular disk, $I_B=\frac{1}{2} M R^2$
For a circular ring, $I_c=M R^2$
$\therefore I_c>I_B>I_A \therefore W_c>W_B>W_A$

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