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

$A$ block starts from rest at the top of a frictionless slide at a height $h_1$ above the ground. The block leaves the slide moving perfectly horizontally at a height $h_2$ above the ground. The block eventually hits the ground travelling at an angle $\theta = 30^\circ$ below the horizontal. Then:

$A$ child stands on the edge of a cliff $10 \ m$ above the ground and throws a stone horizontally with an initial speed of $5 \ m/s$. Neglecting air resistance,the speed with which the stone hits the ground will be $.......... \ m/s$ (given,$g = 10 \ m/s^2$).

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

$A$ ball is thrown from a rooftop at an angle of $45^\circ$ above the horizontal. It hits the ground a few seconds later. At what point during its motion does the ball have $(a)$ greatest speed, $(b)$ smallest speed, and $(c)$ greatest acceleration? Explain.

$A$ fighter plane is flying horizontally at a height of $250\ m$ from the ground with a constant velocity of $500\ m/s$. It passes exactly over a cannon which can fire a shell at any time in any direction with a speed of $100\ m/s$. Find the duration of time for which the plane is in danger of being hit by a cannon shell.