Begin by drawing a diagram of the ball at the moment it is released.
The origin of the reference axis is fixed at the point where the ball
is released, thus
yo = 0 vo
= 0 to = 0
y = -4 ft (final position when it hits
ao = g = -32.2 ft/s2
To determine the velocity when the ball impacts the earth, the time it takes to travel the 4 ft first needs to be calculated.
x(t) = xo + vo (t
- to) + 1/2 ao (t - to)2
t = 0.498 s
The time can now be substituted into the velocity equation,
v = vo + ao (t -
= (-32.2 ft/s2)
v = -16.0 ft/s = -10.9 mi/hr
The negative represents the ball traveling downward in the negative y direction.