A ball is projected upwards from the top of tower with a velocity $50\,\,m{s^{ - 1}}$ making an angle ${30^o}$ with the horizontal. The height of tower is $ 70 \,m$. After how many seconds from the instant of throwing will the ball reach the ground  ........ $\sec$

For angles of projection of a projectile at angle $(45^o  +\theta)$ and $(45^o  -\theta ) $ , the horizontal range described by the projectile are in the ratio of 

A body is projected from the ground at an angle of $45^{\circ}$ with the horizontal. Its velocity after $2s$ is $20 \,ms ^{-1}$. The maximum height reached by the body during its motion is $m$. (use $g =10\, ms ^{-2}$ )

At what angle of elevation, should a projectile be projected with velocity $20 \,ms ^{-1}$, so as to reach a maximum height of $10 \,m$ ?

A projectile is launched from the origin in the $xy$ plane ( $x$ is the horizontal and $y$ is the vertically up direction) making an angle $\alpha$ from the $x$-axis. If its distance. $r =\sqrt{ x ^2+ y ^2}$ from the origin is plotted against $x$, the resulting curves show different behaviours for launch angles $\alpha_1$ and $\alpha_2$ as shown in the figure below. For $\alpha_1, r ( x )$ keeps increasing with $x$ while for $\alpha_2$, $r(x)$ increases and reaches a maximum, then decreases and goes through a minimum before increasing again. The switch between these two cases takes place at an angle $\alpha_c\left(\alpha_1 < \alpha_c < \alpha_2\right)$. The value of $\alpha_c$ is [ignore where $v_0$ is the initial speed of the projectile and $g$ is the acceleration due to gravity]

A ball is thrown at an angle $\theta$ with the horizontal. Its horizontal range is equal to its maximum height. This is possible only when the value of $\tan \theta$ is ..........