$A$ 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 $2 \ s$?

$A$ ball is thrown upwards from the top of a tower $40\,m$ high with a velocity of $10\,m/s$. Find the time when it strikes the ground (in seconds). Take $g = 10\,m/s^2$.

If a ball is thrown vertically upwards with speed $u$,the distance covered during the last $t$ seconds of its ascent is

Galileo's law of odd numbers: "The distances traversed, during equal intervals of time, by a body falling from rest, stand to one another in the same ratio as the odd numbers beginning with unity [namely, $1: 3: 5: 7 \ldots$]". Prove it.

$A$ balloon starts rising from the ground from rest with an upward acceleration of $2 \, m/s^2$. Just after $1 \, s$,a stone is dropped from it. The time taken by the stone to strike the ground is nearly ....... $s$.

$A$ body projected vertically upwards with a velocity $u$ returns to the starting point in $4 \, s$. If $g = 10 \, m/s^2$,the value of $u$ is $......... \, m/s$.