Ball A is thrown upward from the top of a building and takes 12 s to hit the ground. Ball B is thrown

Question

downward with the same speed as Ball A and takes 7 s to hit the ground. How long does it take for ball A to reach it
peak?

Answer 1

Ball A
Hi and Vi
v = Vi - g t
h = Hi + Vi t - 4.9 t^2
when t = 12 , h = 0
0 = Hi + 12 Vi -4.9 (144)
Hi + 12 Vi = 706

Ball B
Vi' = -Vi
Hi = Hi
v = -Vi - g t
0 = Hi - Vi (7) - 4.9 (49)
Hi - 7 Vi = 240

subtract the equations to eliminate Hi
19 Vi = 466
Vi = 24.5 m/s

Now a new problem - we launch a ball up with initial speed 24.5 m/s
how long until v = 0?
v = Vi - gt
0 = 24.5 - 9.81 t
t = 2.5 seconds

Answer 2

Plug and chug, plug and chug :)

Answer 3

1 s

Answer 4

-0.025