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 ............ $m$.

Two balls $A$ and $B$ are thrown with the same velocity $u$ from the top of a tower. Ball $A$ is thrown vertically upwards and ball $B$ is thrown vertically downwards. If a ball $C$ is thrown with the same velocity $u$ in the horizontal direction from the top of the tower,and if $t_A = 6 \ s$ and $t_B = 2 \ s$,then the time $t_C$ taken by ball $C$ to reach the ground is equal to........$s$.

$A$ stone falls freely under gravity. It covers distances $h_1, h_2$ and $h_3$ in the first $5 \ s$,the next $5 \ s$ and the next $5 \ s$ respectively. The relation between $h_1, h_2$ and $h_3$ is:

$A$ body is thrown vertically upwards and takes $5 \text{ s}$ to reach maximum height. The distance travelled by the body will be same in

$A$ ball of mass $m_1$ and another ball of mass $m_2$ are dropped from equal height. If the time taken by the balls are $t_1$ and $t_2$ respectively,then:

$A$ ball dropped from the top of a tower falls the first half of the height of the tower in $10 \, s$. The total time spent by the ball in the air is ......... $s$. [Take $g = 10 \, m/s^2$]