The speed of a projectile at its maximum height is half of its intial speed. The angle of projection is ......... $^o$

A ball is projected with kinetic energy $E$, at an angle of $60^{\circ}$ to the horizontal. The kinetic energy of this ball at the highest point of its flight will become.

An object is projected with a velocity of $20 m/s$ making an angle of $45^o$ with horizontal. The equation for the trajectory is $h = Ax -Bx^2$ where $h$ is height, $x$ is horizontal distance, $A$ and $B$ are constants. The ratio $A : B$ is ($g = 10 ms^{-2}$)

A projectile is fired from the surface of the earth with a velocity of  $5 \,m s^{-1}$ and angle $\theta$ with the horizontal. Another projectile fired from another planet with a velocity of $3 \,m s^{-1}$ at the same angle follows a trajectory which is identical with the trajectory of the projectile fired from the earth. The value of the acceleration due to gravity on the planet is (in $\,m s^{-1}$) is 
(Given $g = 9.8 \,m s^{-2}$) 

A cannon on a level plane is aimed at an angle $\theta $ above the horizontal and a shell is fired with a muzzle velocity ${v_0}$ towards a vertical cliff a distance $D$ away. Then the height from the bottom at which the shell strikes the side walls of the cliff is

Two stones are projected so as to reach the same distance from the point of projection on a horizontal surface. The maximum height reached by one exceeds the other by an amount equal to half the sum of the height attained by them. Then, angle of projection of the stone which attains smaller height is $........$