A ball is dropped from the top of a building which is 39.2m above the level of the sidewalk.

How long does it take for the ball to reach the sidewalk?

hf=hi+vi*t-4.9t^2

0=39.2+0-4.9t^2
solve for time t.

To find the time it takes for the ball to reach the sidewalk, we can use a basic equation of motion. The equation we can use is:

h = 1/2 * g * t^2

Where:
- h is the height of the building (39.2m in this case),
- g is the acceleration due to gravity (approximately 9.8 m/s^2),
- t is the time it takes for the ball to reach the sidewalk (what we want to find).

By rearranging the equation, we have:

t = sqrt(2 * h / g)

Plugging in the given values, we can calculate the time it takes for the ball to hit the sidewalk:

t = sqrt(2 * 39.2 / 9.8)
t = sqrt(78.4 / 9.8)
t = sqrt(8)

Therefore, the time it takes for the ball to reach the sidewalk is approximately 2.83 seconds.