. 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

in physics zero. in muscle fatigue could be high