An object is thrown vertically upward with a speed of $30 \,m/s$. The velocity of the object half-a-second before it reaches the maximum height is (in $\,m/s$)

When a ball is dropped into a lake from a height $4.9 \, m$ above the water level,it hits the water with a velocity $v$ and then sinks to the bottom with the constant velocity $v$. It reaches the bottom of the lake $4.0 \, s$ after it is dropped. The approximate depth of the lake is ............ $m$.

$A$ stone is dropped from a certain height and reaches the ground in $5 \ s$. It is stopped after $3 \ s$ of its fall and then released again. The total time taken by the stone to reach the ground will be .... $s$

$A$ body is dropped from a height $H$. The time taken to cover the second half of the journey is:

$A$ ball is projected upwards from a height $h$ above the surface of the earth with velocity $v$. The time at which the ball strikes the ground is

$A$ ball is thrown vertically downward with a velocity of $5 \ m/s$. With what velocity should another ball be thrown downward after $2 \ s$ so that it can hit the $1^{st}$ ball in $2 \ s$?