At the top of the trajectory of a projectile,the acceleration is

$A$ body is projected from the earth at an angle of $30^{\circ}$ with the horizontal with some initial velocity. If its range is $20 \ m$, the maximum height reached by it is: (in meters)

The maximum range of a gun on horizontal terrain is $16 \, km$. If $g = 10 \, m/s^2$,what must be the muzzle velocity of the shell in $m/s$?

What is the angle between the velocity and acceleration of a projectile at its maximum height (in $°$)?

Two projectiles of same mass and with same velocity are thrown at an angle $60^o$ and $30^o$ with the horizontal,then which quantity will remain same?

$A$ particle is projected with speed $u$ at an angle $\theta$ with the horizontal from the ground. If it is at the same height from the ground at times $t_1$ and $t_2$,then its average velocity in the time interval $t_1$ to $t_2$ is .........