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

Two particles are projected from the same point with the same speed $u$ such that they have the same range $R$,but different maximum heights,$h_1$ and $h_2$. Which of the following is correct?

$A$ ball thrown by a boy is caught by another after $2 \ s$ at the same level some distance away. If the angle of projection is $30^o$,the velocity of projection is ......... $m/s$.

$A$ water fountain on the ground sprinkles water all around it. If the speed of water coming out of the fountain is $v$,the total area around the fountain that gets wet is :

For a projectile,the ratio of the maximum height reached to the square of the time of flight is:

$A$ ball is thrown from the location $(x_0, y_0) = (0, 0)$ of a horizontal playground with an initial speed $v_0$ at an angle $\theta_0$ from the $+x$-direction. The ball is to be hit by a stone,which is thrown at the same time from the location $(x_1, y_1) = (L, 0)$. The stone is thrown at an angle $(180^{\circ} - \theta_1)$ from the $+x$-direction with a suitable initial speed $v$. For a fixed $v_0$,when $(\theta_0, \theta_1) = (45^{\circ}, 45^{\circ})$,the stone hits the ball after time $T_1$,and when $(\theta_0, \theta_1) = (60^{\circ}, 30^{\circ})$,it hits the ball after time $T_2$. In such a case,$(T_1 / T_2)^2$ is. . . . .