Q41 / 60 · JEE Advanced 2012 (Paper 2) · Physics

Two identical discs of same radius $R$ are rotating about their axes in opposite directions with the same constant angular speed $\omega$. The discs are in the same horizontal plane. At time $t=0$, the points $P$ and $Q$ are facing each other as shown in the figure. The relative speed between the two points $P$ and $Q$ is $v_{r}$. In one time period $(T)$ of rotation of the discs, $v_{r}$ as a function of time is best represented by Figure

  • Correct answer
    A
    Figure
  • B
    Figure
  • C
    Figure
  • D
    Figure

Solution

At $t=0, t=\frac{T}{2}$ and $t=T$ therelative velocity will bezero. At $t=\frac{T}{4}$ and $t=\frac{3 T}{4}$, the relative velocity will be maximum in magnitude Hence graph (a) correctly depicts $v_{r}$ versus $t$ graph.

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

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