A ball is thrown vertically upwards from the top of a tower with a velocity $u$. This ball reaches the ground level with a velocity $4\,u$. The height of the tower is

- A
$\frac{3u^2}{g}$

- B
$\frac{4u^2}{g}$

- C
$\frac{6u^2}{g}$

- D
$\frac{15u^2}{2g}$

A ball is dropped from the top of a building of height $80 \,m$. At same instant another ball is thrown upwards with speed $50 \,m / s$ from the bottom of the building. The time at which balls will meet is ........ $s$

A parachutist after bailing out falls $50\, m$ without friction. When parachute opens, it decelerates at $2\, m/s^2$. He reaches the ground with a speed of $3\, m/s$. At what height, did he bail out ........... $m$

A ball is thrown upwards. Its height varies with time as follows If the acceleration due to gravity is $7.5\, m/s^2$, then the height $h$ is.........$m$

- [AIIMS 2011]

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 $=340 \,m / s$ )

- [KVPY 2015]

A ball is dropped from a height $h$ above ground. Neglect the air resistance, its velocity $(v)$ varies with its height above the ground as