Answer:
6.46
Step-by-step explanation:
h(t) = (1/2)[tex]att^{2}[/tex] + v0t + h0
Origin is at surface of water (h = 0), up is positive.
a = -g = -9.8 m/[tex]s^{2}[/tex]
v0 = 25 m/s
h0 = 50 m
h(t) = -4.9t2 + 25t + 50
Find t when
7 = [tex]-4.9t^{2}[/tex] + 25t + 50
[tex]4.9t^{2}[/tex] - 25t - 43 = 0
t = [1/(2*4.9)] [25 ±√([tex]25^{2}[/tex] + 4*4.9*43)]
t = (0.102)(25 ± 38.312)
t > 0 ⇒ use only the positive square root
t = (0.102)(25 + 38.312) ≅ 6.46 s
It is 7m above the water at about 6.46 s
