Question

a ball is thrown vertically upward with a velocity u from the top of a tower. If it strikes the ground with velocity 3u the time taken by the ball to reach the ground is

Answer 1

Here we make use of the formula $v=u+at$, here $v$ final velocity, $u$ initial velocity, $a$ acceleration ( in the direction of velocity is taken as positive) and $t$ time taken.

The time taken by the ball to reach the top most point (when the velocity becomes 0) is given by

$u-gt_1=0\\ t_1=\frac{u}{g}$

The time taken to reach a velocity $3u$ from an initial velocity of 0 is

$3u=0+gt_2\\ t_2=\frac{3u}{g}$

The time taken by the ball to reach the ground, after throwing from the top of the tower is
$t=t_1+t_2\\ t=\frac{u}{g}+\frac{3u}{g} \\ t=\frac{4u}{g}$

Answer 2

Explanation:

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