Dear Aspirant,

For a circle with r radius, circumference will be 2*pi*r, and therefore the distance travelled = pi*r that is half the circumference.

For the displacement part, the particle will travel along the radius from one end to the other = 2*r(diameter).

Ratio(d/s) = pi*r/2*r = pi/2.

HOPE THIS HELPS. THANK YOU.