A particle is moving along a vertical circle of radius $R=20 \text{m}$ with a constant speed $v=31.4 {\text{\hspace{0.17em}\hspace{0.17em}ms}}^{-1}$ as shown in Fig. Straight line ABC is horizontal and passes through the centre of the circle.  A shell is fired from point A at the instant when particle is at  C. 
If distance AB is $20\sqrt{3} \text{m}$ and shell collides with the particle at  B, ( $\pi =3.14$ and  $g=10{\text{\hspace{0.17em}m/s}}^2$)