. Desde el borde de una azotea de un edificio, se lanza un cuerpo hacia abajo con una velocidad de 20 m/s, si el edificio mide 105 m. ¿Cuántos segundos dura la caída?

t = 3.01 s

Explanation:

In order to calculate how long it takes to the object to fall to the ground, you use the following formula, for the calculation of the height:

   (1)

yo: height of the building = 105 m

vo: initial velocity of the body = 20m/s

g: gravitational acceleration = 9.8m/s^2

t: time = ?

To find the time t, you take into account that when the body arrives to the ground the height is zero, that is, y = 0.

You replace the values of all parameters in the equation (1), and you obtain a quadratic polynomial for t:

Next, you use the quadratic formula to get the roots of the polynomial:

a = -4.9

b = -20

c = 105

You choose the positive value t1, because it has physical meanning.

Hence, the body takes 3.01s to arrive to the ground

good looking response