Calculate the velocity and the time for a ball to strike the ground if the ball is dropped from the top of 40 m tall building

Since to calculate velocity, we need to know the time,
we'll determine the time first.

To calculate the time,
we'll use the equation:

x - x0 = v0*t + a*t^2/2
(1)

x - x0 is the distance covered by the ball when it's
dropped from the top of the building.

Since the building is
40 m tall, then the distance is the height of the
building.

x - x0 = 40m

The
original velocity is 0, v0 = 0.

The acceleration is g = 9.8
m/s^2

We'll substitute all these values in
(1):

40 = 0 + 9.8*t^2/2

 80 =
9.8*t^2

We'll divide by 9.8 and we'll get the
time:

t^2 = 80/9.8

t = 2.85 s
approx.

round
t

t = 2.9
s

Now, we can calculate the velocity,
because we've get the time:

v = v0 +
g*t

v = g*t

v =
9.8*2.9

v = 28
m/s