The equation of a projectile is $y=\sqrt{3} x-\frac{ x^2}{2}$, the velocity of projection is

Two projectiles $A$ and $B$ are thrown with initial velocities of $40\,m / s$ and $60\,m / s$ at angles $30^{\circ}$ and $60^{\circ}$ with the horizontal respectively. The ratio of their ranges respectively is $\left( g =10\,m / s ^2\right)$

A piece of marble is projected from earth's surface with velocity of $19.6 \sqrt{2}\,m / s$ at $45^{\circ}.$ $2\,s$ later its velocity makes an angle $\alpha$ with horizontal, where $\alpha$ is $..........$

A cricketer can throw a ball to a maximum horizontal distance of $100 \,m$. With the same effort, he throws the ball vertically upwards. The maximum height attained by the ball is  ......... $m$

A heavy particle is projected from a point on the horizontal at an angle $60^o$ with the horizontal with a speed of $10\ m/s$ . Then the radius of the curvature of its path at the instant of crossing the same horizontal will be    ......... $m$

A small boy is throwing a ball towards a wall $6 \,m$ in front of him. He releases the ball at a height of $1.4 \,m$ from the ground. The ball bounces from the wall at a height of $3 \,m$, rebounds from the ground and reaches the boy's hand exactly at the point of release. Assuming the two bounces (one from the wall and the other from the ground) to be perfectly elastic, .......... $m$ far ahead of the boy did the ball bounce from the ground