(d) Net displacement in one loop = 0
Average velocity $= \frac{net\ displacement}{time} = \frac{0}{t} = 0$
Distance travelled in one rotation (loop) = $2\pi r$
$\therefore Average\ speed = \frac{distance}{time} = \frac{2\pi r}{t}$
$= \frac{2 \times 3.14 \times 100}{62.8} = 10m/s.$