At what point of a projectile motion acceleration and velocity are perpendicular to each other

A projectile is thrown upward with a velocity $v_0$ at an angle $\alpha$ to the horizontal. The change in velocity of the projectile when it strikes the same horizontal plane is

The path of a projectile in the absence of air drag is shown in the figure by dotted line. If the air resistance is not ignored then which one of the path shown in the figure is appropriate for the projectile

A projectile projected at an angle ${30^o}$ from the horizontal has a range $2\upsilon ,\,\sqrt 2 \upsilon \,\,{\rm{ and}}\,{\rm{zero}}$. If the angle of projection at the same initial velocity be ${60^o}$, then the range will be

A ball is projected from a point $O$ as shown in figure. It will strike the ground after ........ $s$ $\left(g=10 \,m / s ^2\right)$

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