$A$ stone falls freely under gravity. It covers distances $d_1$ and $d_2$ in the first $4$ seconds and the next $8$ seconds, respectively. The ratio $\frac{d_2}{d_1}$ is

An iron block is dropped into a deep well. The sound of the splash is heard after $4.23 \, s$. If the depth of the well is $78.4 \, m$,find the speed of sound in air in $m/s$ $\left(g = 9.8 \, m/s^2\right)$.

$A$ body thrown vertically upwards from the ground reaches a maximum height $H$. The ratio of the velocities of the body at heights $\frac{3H}{4}$ and $\frac{8H}{9}$ from the ground is

$A$ packet is dropped from a balloon which is going upwards with a velocity of $12 \, m/s$. The velocity of the packet after $2 \, s$ will be ........ $m/s$.

Two balls $A$ and $B$ are placed at the top of a $180 \,m$ tall tower. Ball $A$ is released from the top at $t = 0 \,s$. Ball $B$ is thrown vertically downward with an initial velocity $u$ at $t = 2 \,s$. Both balls meet at a point $100 \,m$ above the ground. Find the value of $u$ in $m \,s^{-1}$. [Use $g = 10 \,m \,s^{-2}$]

From the top of a $64\, ft$ high tower,a stone is thrown upwards vertically with the velocity of $48\, ft/s$. The greatest height (in $ft$) attained by the stone,assuming the value of the gravitational acceleration $g = 32\, ft/s^2$,is