$A$ stone thrown upward with a speed $u$ from the top of a tower reaches the ground with a velocity $3u$. The height of the tower is (in $u^2/g$)

An object is thrown vertically upward with a speed of $30 \,m/s$. The velocity of the object half-a-second before it reaches the maximum height is (in $\,m/s$)

$A$ projectile is fired vertically upwards with an initial velocity $u$. After an interval of $T$ seconds,a second projectile is fired vertically upwards,also with initial velocity $u$.

$A$ particle is projected upwards. The times corresponding to height $h$ while ascending and while descending are $t_1$ and $t_2$ respectively. The velocity of projection will be

Two balls of the same size,but where the density of one is greater than that of the other,are dropped from the same height. Which ball will reach the Earth first (air resistance is negligible)?

$A$ 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 $g = 9.8\,m/s^2$)