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JEE Main 2013 · Rolling Motion

Rolling Motion question from JEE Main 2013

Q81JEE Main 2013Difficult

Rolling Motion

A hoop of radius rr and mass mm rotating with an angular velocity ω0\omega_0 is placed on a rough horizontal surface. The initial velocity of the center of the hoop is zero. What will be the velocity of the center of the hoop when it ceases to slip?

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Answer: (c)

  1. Friction acts at the contact point, so angular momentum about the contact point is conserved.
  2. Initial: Iω0=mr2ω0I\omega_0 = mr^2\omega_0. Final (rolling): mvr+mr2vr=2mvrmvr + mr^2\dfrac{v}{r} = 2mvr.
  3. mr2ω0=2mvr⇒v=rω02mr^2\omega_0 = 2mvr \Rightarrow v = \dfrac{r\omega_0}{2}.
  4. So the answer is (c).
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