$S=20\pi{}\ t^2\ cm $ $v=\dfrac{dS}{dt}=40\pi{}\ t\ cm/sec $ $a_t=\dfrac{dv}{dt}=40\pi{}\ cm/{sec}^2 $ $Radius=20\ cm\ \therefore{}for\ one\ revolution;S=2\pi{}(20) $ $\therefore{}\ 2\pi{}\left(20\right)=20\pi{}\ t^2 %eq1$ $\therefore{}\ t^2=2\ \&\ t=\sqrt{2}\ second. $ Velocity at $t=\sqrt{2} $ is given by; $v=(40\pi{})\sqrt{2}\ cm/sec $ Normal Acceleration: $a_n=\dfrac{v^2}{\rho{}}=\dfrac{{40}^2\times{}{\pi{}}^2\times{}2}{20} $ $\therefore{}\ a_n=1579.14\ cm/{sec}^2 $ Tangential Acceleration: $a_t=40\ \pi{} $ $\therefore{}\ a_n=125.66\ cm/sec $