## Statement

difficulty A glass of water on the edge of a table falls towards the floor from a height of 1.5 m. Considering that gravity is 10 m/s2, calculate:

a) The time the glass is in the air.
b) The velocity with which it impacts on the ground.

## Solution

Question a)

Data

H = 1.5 m
When it gets to the ground y = 0 m.
g = 10 m/s2

Resolution

To answer this question simply apply the position equation in free fall and solve for time when the glass is at y = 0 m, that is, when it reaches the ground:

$y=H-\frac{g·{t}^{2}}{2}⇒\phantom{\rule{0ex}{0ex}}t=\sqrt{\frac{-2·\left(y-H\right)}{g}}⇒\phantom{\rule{0ex}{0ex}}t=\sqrt{\frac{-2·\left(0-1.5\right)}{10}}⇒\phantom{\rule{0ex}{0ex}}t=\sqrt{\frac{3}{10}}⇒\phantom{\rule{0ex}{0ex}}\overline{)t=0.55}$

Question b)

Data

H = 1.5 m
When it gets to the ground y = 0 m.
g = 10 m/s2
Time that it takes to reach the ground t = 0.55 s

Resolution

Since we know the time that it takes reaching the floor, it is enough to apply the equation of velocity for that time:

## Formulas worksheet

These are the main formulas that you must know to solve this exercise. If you are not clear about their meaning, we recommend you to check the theory in the corresponding sections. Furthermore, you will find in them, under the Formulas tab, the codes that will allow you to integrate these equations in external programs like Word or Mathematica.

Formulas
Related sections
$y=\mathrm{H}-\frac{1}{2}g{t}^{2}$
$v=-g\cdot t$