A particle is moving in a circle of radius R with constant speed. It covers an angle $ \theta $ in some time interval. Find displacement in this interval of time
$ \triangle S = \sqrt { R^2 + R^2 - 2R^2 cos \theta } $ $ \triangle S= \sqrt { 2R^2 - 2R^2 Cos \theta } = \sqrt { 2R^2 (1 - Cos \theta ) }$ $ = 2 R sin { \theta \over 2 } $