Initial/final velocity?

Question

I have a couple of math problems that I believe are interrelated with physics, and I'm not really sure how to solve these problems.

A person drops a ball onto the dirt below. Use this position function to solve the problem: -16t^2 + (initial velocity)(time) + initial height

How high is the wall if the ball hits the dirt 3 seconds after the ball is dropped?

What's the velocity of the ball when it hits the ground?

Answer 1

y=position.wrt ground level in feet.
y=-16t^2+ut+h
u=0,t=3s
y=-144+h
if y=0, h=144
v=dy/dt=-32t+u=-96+0=-96ft/s

Answer 2

Initial velocity is zero since the ball is just dropped.
Initial height is w = height of wall.
s = -16t^2 +w [s = position at any time t
When t = 3, s = 0
So w = 144 feet
v = ds/dt = -32t = -96 ft/sec when it strikes ground, which means it is ging 96 ft/sec in a downward direction..