physics
posted by student .
A rock is thrown vertically upward with a speed of 14.0 m/s from the roof of a building that is 50.0 m above the ground. Assume free fall.
In how many seconds after being thrown does the rock strike the ground? in s
What is the speed of the rock just before it strikes the ground? in m/s

Vf^2 = Vo^2 + 2gd,
d = 50 + (Vf^2  Vo^2) / 2g,
d = 50 + (0  (14)^2) / 19.6,
d = 50 + 10 = 60m above ground.
Vf = Vo + gt,
t(up) = (Vf  Vo) / a,
t(up) = (0  14) / 9.8 = 1.43s.
d = Vo*t + 0.5gt^2 = 60m.
0 + 0.5*9.8t^2 = 60,
4.9t^2 = 60,
t^2 = 12.24,
t(down) = 3.50s.
T = t(up) + t(down),
T = 1.43 + 3.50 = 4.93s