SOLUTION: Use the equation: h = 5t^2 +vt + c h= HEIGHT v= VELOCITY t= TIME c= distance thrown from A rock fall off a cliff 80 meters from the ground. How long does it take for the r

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Question 612617: Use the equation: h = 5t^2 +vt + c
h= HEIGHT
v= VELOCITY
t= TIME
c= distance thrown from

A rock fall off a cliff 80 meters from the ground. How long does it take for the rock to hit the ground?
Answer by Alan3354(69443) About Me  (Show Source):
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Use the equation: h = 5t^2 +vt + c
h= HEIGHT
v= VELOCITY
t= TIME
c= distance thrown from

A rock fall off a cliff 80 meters from the ground. How long does it take for the rock to hit the ground?
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Heights are measured from the ground up.
If something falls, its height decreases.
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Use the equation: h = -5t^2 +vt + c (-5, not +5)
h(t) = -5t^2 + 0t + 80
It hits the ground when h(t) = 0
h(t) = -5t^2 + 0t + 80 = 0
5t^2 = 80
t^2 = 16
t = 4 seconds