Discuss the observation of Galileo for objects falling freely.

Due to the presence of air resistance, if a body dropped from a height of $20 \ m$ reaches the ground with a speed of $18 \ m/s$, then the time taken by the body to reach the ground is nearly (in $s$)

$A$ body starts to fall freely under gravity. The distances covered by it in the first,second,and third seconds are in the ratio:

An $NCC$ parade is moving at a uniform speed of $9\,km/h$ under a mango tree on which a monkey is sitting at a height of $19.6\,m$. At a particular instant,the monkey drops a mango. $A$ cadet will receive the mango if their distance from the tree at the time of the drop is $...m$ (Given $g = 9.8\,m/s^2$)

With what velocity should a ball be projected vertically so that the distance covered by it in the $5^{th}$ second is twice the distance it covers in its $6^{th}$ second? (Take $g = 10 \, m/s^2$)

$A$ ball is projected vertically up from the ground. Boy $A$, standing at the window of the first floor of a nearby building, observes that the time interval between the ball crossing him while going up and the ball crossing him while going down is $2 \ s$. Another boy $B$, standing on the second floor, notices the time interval between the ball passing him twice, during up and down motion, is $1 \ s$. Calculate the difference between the vertical positions of boy $B$ and boy $A$. (Assume $g = 10 \ m \ s^{-2}$) (in $m$)