# Rotating disks

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

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