A ball is dropped from a roof to the ground 4.00 m below. Exactly 0.400 s later, a rock is thrown downwards with some initial velocity. If the two objects hit the ground at exactly the same time, what was the initial speed of the rock?
d = Vo*t + 0.5g*t^2 = 4m
0 + 4.9t^2 = 4,
t^2 = 0.8163,
t1 = 0.90s.
t2 = 0.9 - 0.4 = 0.50s.
d = Vo*t + 0.5g*t^3 = 4,
0.5Vo + 4.9*(0.5)^2 = 4,
0.5V0 + 1.225 = 4,
0.5Vo = 2.775,
Vo = 5.55m/s.