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JEE Advanced 2023Paper 2
Exam
JEE Advanced
Year
2023
Paper
Paper 2
Subject
Physics
Chapter
Rotational Motion

JEE Advanced 2023 · Paper 2 · Physics · Rotational Motion

An annular disk of mass M , inner radius a and outer radius b is...

An annular disk of mass MM, inner radius aa and outer radius bb is placed on a horizontal surface with coefficient of friction μ\mu, as shown in the figure. At some time, an impulse J0x∧{J}_{0}\overset{∧}{x} is applied at a height hh above the center of the disk. If h=hmh = {h}_{m} then the disk rolls without slipping along the xx-axis. Which of the following statement(s) is(are) correct?

An annular disk of mass M , inner radius a and outer radius b is placed on a horizontal surface with coefficient of

Options

  1. AFor μ≠0\mu \ne 0 and a→0,hm=b2a \to 0, {h}_{m} = \dfrac{b}{2}
  2. BFor μ≠0\mu \ne 0 and a→b,hm=ba \to b, {h}_{m} = b
  3. CFor h=hmh = {h}_{m}, the initial angular velocity does not depend on the inner radius aa
  4. DFor μ=0\mu = 0 and h=0h = 0, the wheel always slides without rolling

Correct answer

A. For μ≠0\mu \ne 0 and a→0,hm=b2a \to 0, {h}_{m} = \dfrac{b}{2}

Step-by-step solution

As we know, J→=∆P→\overset{\to}{J} = ∆ \overset{\to}{P}

⇒J0=MV...(i)⇒ {J}_{0} = MV . . . \left(i\right)

An annular disk of mass M , inner radius a and outer radius b is placed on a horizontal surface with coefficient of

About center of the disk, we can also write

J0×h=ICMω⇒J0×h=[M2(a2+b2)]ω...(ii){J}_{0} \times h = {I}_{CM}\omega ⇒ {J}_{0} \times h = \left[\dfrac{M}{2}\left({a}^{2} + {b}^{2}\right)\right]\omega . . . \left(ii\right)

If h=hm⇒ω=Vb(pure rolling)h = {h}_{m} ⇒ \omega = \dfrac{V}{b}\left(\text{pure rolling}\right)

From equation(ii), we can write

⇒J0×hm=(M2)(a2+b2)Vb...(iii)⇒ {J}_{0} \times {h}_{m} = \left(\dfrac{M}{2}\right)\left({a}^{2} + {b}^{2}\right)\dfrac{V}{b} . . . \left(iii\right)

By dividing equation (i)( i ) with the equation (iii)( iii ), we get

⇒hm=a2+b22b⇒ {h}_{m} = \dfrac{{a}^{2} + {b}^{2}}{2b}

Now, considering all cases:

If a→0⇒hm=b2a \to 0 ⇒ {h}_{m} = \dfrac{b}{2}

If a→b⇒hm=ba \to b ⇒ {h}_{m} = b

If h=hm⇒ωh = {h}_{m} ⇒ \omega is independent of aa(As we get ω=Vb\omega = \dfrac{V}{b})

If μ=0andh=0⇒\mu = 0\text{and}h = 0 ⇒Wheel will slide without rolling.

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