$A$ stone is projected at an angle of $60^o$ from the ground level and strikes at an angle of $30^o$ on the roof of a building of height $h = 30 \, m$. Find the speed of projection (in $m/s$) of the stone.

There are three steps,each with a height of $10 \, cm$ and a width of $20 \, cm$. What minimum horizontal velocity (in $m/s$) must be given to a ball from the top step so that it clears all three steps?

$A$ ball is thrown upward from the top of a building at an angle of $30^{\circ}$ to the horizontal and with an initial speed of $20 \,m/s$. If the ball strikes the ground after $3 \,s$, then the height of the building is (acceleration due to gravity $g = 10 \,m/s^2$) (in $\,m$)

$A$ 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.

An aeroplane moving horizontally at a speed of $200 \; m/s$ and at a height of $8 \; km$ is to drop a bomb on a target. At what horizontal distance from the target should the bomb be released? (Take $g = 9.8 \; m/s^2$)

Water is flowing from a horizontal pipe fixed at a height of $2\,m$ from the ground. If it falls at a horizontal distance of $3\,m$ as shown in the figure,the speed of water when it leaves the pipe is $............\,ms^{-1}$ (take $g=9.8\,ms^{-2}$).