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)?

$A$ body falling from rest has a velocity $v$ after it falls through a height $h$. The distance it has to fall down further for its velocity to become double,will be $...............\,h$.

$A$ body falls freely for $10 \ s$. What is its average velocity during this journey (in $m/s$)? (Take $g = 10 \ m/s^2$)

$A$ stone is dropped from a certain height and reaches the ground in $5\, s$. If the stone is stopped after $3\, s$ of its fall and then allowed to fall again,then the time taken by the stone to reach the ground for the remaining distance is........$s$.

From $18 \text{ m}$ height above the ground, a ball is dropped from rest. The height above the ground at which the magnitude of velocity equals the magnitude of acceleration (in the same set of units) due to gravity is . . . . . . $\text{m}$. (Take $g = 10 \text{ m/s}^2$ and neglect the air resistance)

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 $g = 10 \, m/s^2$)