MCQ
An annular disk of mass $M$, inner radius $a$ and outer radius $b$ is placed on a horizontal surface with coefficient of friction $\mu$, as shown in the figure. At some time, an impulse $J_0 \hat{x}$ is applied at a height $\mathrm{h}$ above the center of the disk. If $h=h_m$ then the disk rolls without slipping along the $x$-axis. Which of the following statement(s) is(are) correct?

(image)

($A$) For $\mu \neq 0$ and $a \rightarrow 0, h_m=b / 2$

($B$) For $\mu \neq 0$ and $a \rightarrow b, h_m=b$

($C$) For $h=h_m$, the initial angular velocity does not depend on the inner radius $a$.

($D$) For $\mu=0$ and $h=0$, the wheel always slides without rolling.

  • A
    $A,D$
  • B
    $A,B$
  • C
    $A,B,C$
  • $A,B,C,D$

Answer

Correct option: D.
$A,B,C,D$
d
$\mathrm{J}_0=\mathrm{mv} \ldots . .(1)$

$\mathrm{J}_0 \mathrm{~h}_{\mathrm{m}}=\mathrm{I}_{\mathrm{c}} \omega \ldots \ldots .(2)$

$\mathrm{v}=\omega \mathrm{R} \ldots \ldots .(3)$

$\Rightarrow \mathrm{h}_{\mathrm{m}}=\frac{\mathrm{I}_{\mathrm{c}}}{\mathrm{mR}}$

$(A)$ If $\mathrm{a}=0 \mathrm{I}_{\mathrm{c}}=\frac{1}{2} \mathrm{mb}^2 \& \mathrm{R}=\mathrm{b} \quad \therefore \mathrm{h}_{\mathrm{m}}=\frac{\mathrm{b}}{2}$

$(B)$ If $\mathrm{a}=\mathrm{b} \mathrm{I}_{\mathrm{C}}=\mathrm{mb}^2 \& \mathrm{R}=\mathrm{b} \therefore \mathrm{h}_{\mathrm{m}}=\mathrm{b}$

$(C)$ $\mathrm{v}=\frac{\mathrm{J}_0}{\mathrm{~m}} \Rightarrow 100=\frac{\mathrm{V}}{\mathrm{R}}=\frac{\mathrm{J}_0}{\mathrm{mR}}$

$(D)$ Force is acting on COM $\therefore$ No rotation.

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