physics, please help me, this question is hard
posted by andrew on .
John Stands at the edge of a flat roof of a three story building and throws a 180g ball straight up into the air that reaches a height of 3.0 meters above the roof. ( building is 14 meters high)
A. What is the initial speed of the ball?
B. How long does it take to reach it's maximum height?
C. Assuming it misses the building on it's way down, at what speed does it hit the ground? ( building is 14 meters high)
D. What is the total length of the time the ball is in the air?
E. What is the intitial momentum of the ball?
F. What is the momentum of the ball at its peak?
G. What is the momentum of the ball when it hits the ground?
Thank you!

a. Vf^2 = Vi^2 + 2*a*d
solve for Vi given Vf = 0 (speed at max height is 0), a = 9.81 m/s^2 and d = 3m.
b. Once you know Vi, you can use
Vf = a*t + Vi and solve for t.
(once again, Vf = 0 since you're only considering the path of the ball from the top of the building to maximum height)
c. Vf^2 = Vi^2 + 2*a*d
(d = height of building + 3m)
d. Vf = a*t + Vi
Use your answer from part c. to solve for the time it takes the ball to fall from max height to the ground and then add your answer from part b. to get the total time.
e,f,g: momentum = m*v