A stone is projected with a velocity $20 \sqrt{2}\,m / s$ at an angle of $45^{\circ}$ to the horizontal. The average velocity of stone during its motion from starting point to its maximum height is $..........\,m/s$ (take $g=10\,m / s ^2$ )

A cricket ball is thrown at a speed of $28\; m /s$ in a direction $30^o$ above the horizontal. Calculate

$(a)$ the maximum height,

$(b)$ the time taken by the ball to return to the same level, and

$(c)$ the distance from the thrower to the point where the ball returns to the same level

Given below are two statements. One is labelled as Assertion $A$ and the other is labelled as Reason $R$.

Assertion A :Two identical balls $A$ and $B$ thrown with same velocity '$u$ ' at two different angles with horizontal attained the same range $R$. If $A$ and $B$ reached the maximum height $h_{1}$ and $h_{2}$ respectively, then $R =4 \sqrt{ h _{1} h _{2}}$

Reason R: Product of said heights.

$h _{1} h _{2}=\left(\frac{u^{2} \sin ^{2} \theta}{2 g }\right) \cdot\left(\frac{u^{2} \cos ^{2} \theta}{2 g }\right)$

Choose the $CORRECT$ answer 

The initial speed of a projectile fired from ground is $u$. At the highest point during its motion, the speed of projectile is $\frac{\sqrt{3}}{2} u$. The time of flight of the projectile is:

$K_i :$ initial kinetic energy

$K_h :$ kinetic energy at the highest point

A projectile crosses two walls of equal height $H$ symmetrically as shown The maximum height of the projectile is  ........ $m$