Answer:
energy? or power? I'm not really sure but using the quizzes app really help with science problems
Answer:
Acceleration, 
Explanation:
Given that,
Height from a ball falls the ground, h = 17.3 m
It is in contact with the ground for 24.0 ms before stopping.
We need to find the average acceleration the ball during the time it is in contact with the ground.
Firstly, find the velocity when it reached the ground. So,

u = initial velocity=0 m/s
a = acceleration=g

It is in negative direction, u = -18.41 m/s
Let a is average acceleration of the ball. Consider, v = and u = -18.41 m/s.

So, the average acceleration of the ball during the time it is in contact is
.
My very eager mother just served us nine pizzas
The force pushing down is the force of Gravity. On a chair it is in perfect balance with the force pushing up (the normal force)
in terms of magnitude
FN = FG = mg
the forces are in opposite direction
hope this helps