Originally Posted by

**gordonmckee** A ball is thrown down at 72 km h–1 speed from the top of a building. The

building is 125 metres tall. The distance travelled before it reach the

ground is as follows,

s = u0t + 1/2gtsquared

where:

u0 = initial velocity (ms -1)

g = acceleration due to gravity (10 ms -2)

t = time (s)

Find the time for the ball to drop to fifth of the height of the building.

$\displaystyle \color{red}{100 = 72t + 5t^2}$

&

Find the time for the ball to reach the ground.

$\displaystyle \color{red}{125 = 72t + 5t^2}$