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 is thrown vertically upwards with a velocity of $19.6 \, ms^{-1}$. The position of the body after $4 \, s$ will be

$A$ body is projected vertically upward with a speed of $40 \, m/s$. The distance travelled by the body in the last second of its upward journey is ........... $m$. [Take $g = 9.8 \, m/s^2$ and neglect the effect of air resistance]

$A$ ball is dropped vertically from a height of $h$ onto a hard surface. If the ball rebounds from the surface with a fraction $r$ of the speed with which it strikes the latter on each impact,what is the net distance travelled by the ball up to the 10th impact?

$A$ man throws balls with the same speed vertically upwards one after the other at an interval of $2\,s$. What should be the speed of the throw so that more than two balls are in the sky at any time? (Given $g = 9.8\,m/s^2$)

$Assertion$ : Two balls of different masses are thrown vertically upward with the same speed. They will pass through their point of projection in the downward direction with the same speed.
$Reason$ : The maximum height and downward velocity attained at the point of projection are independent of the mass of the ball.