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)?

$A$ particle is thrown vertically upwards. It passes the same height at $t_1 = 2 \; s$ and $t_2 = 10 \; s$. The height is:

$A$ boy is standing on top of a tower of height $85 \, m$ and throws a ball in the vertically upward direction with a certain speed. If $5.25 \, s$ later he hears the ball hitting the ground,then the speed with which the boy threw the ball is .......... $m/s$ (take $g = 10 \, m/s^2$ and speed of sound in air $= 340 \, m/s$).

$A$ ball is thrown vertically upwards from the top of a tower at $4.9 \ m/s$. It strikes the pond near the base of the tower after $3 \ s$. The height of the tower is........$m$

$A$ stone is shot straight upward with a speed of $20\, m/s$ from a tower $200\, m$ high. The speed with which it strikes the ground is approximately........$m/s$.

Water drops are falling from a nozzle of a shower onto the floor,from a height of $9.8\, m$. The drops fall at a regular interval of time. When the first drop strikes the floor,at that instant,the third drop begins to fall. Locate the position of the second drop from the floor when the first drop strikes the floor. (In $m$)