(C)
Explanation:
The circle has a radius r = 0.5 m, which means that its circumference C is
[tex]C = 2\pi r = 2\pi(0.5\:\text{m}) = 3.14\:\text{m}[/tex]
One revolution means that the stopper travels a distance equal to the circumference of the circle so the velocity of the stopper is
[tex]v = \dfrac{C}{t} =\dfrac{3.14\:\text{m}}{0.2\:\text{s}} = 15.7\:\text{m/s} \approx 16\:\text{m/s}[/tex]
