Question 987005
A small rock sits on the edge of a tall building.
 A strong wind blows the rock off the edge.
 The distance, in feet, between the rock and the ground t seconds after the rock leaves the edge is given by d = −16t^2 − 5t + 470.
If the answer is not an integer, enter it as a decimal. Round to the nearest hundredth
:
From the given formula we can surmise that the cliff is 470 above the ground below, which is the reference; d = 0
:
How many seconds after the rock leaves the edge is it 446feet from the ground?
−16t^2 − 5t + 470 = 446
−16t^2 − 5t + 470 - 446 = 0
−16t^2 − 5t + 24 = 0
Using the quadratic formula {{{x = (-b +- sqrt( b^2-4*a*c ))/(2*a) }}}, where
a = -16; b = -5; c = 24
I got a positive solution of s = 1.08 seconds
:
How many seconds after the rock leaves the edge does it hit the ground?
d = 0
−16t^2 − 5t + 470 = 0
Now a = -16; b = -5; c = 470
I got a positive solution of s = 5.27 seconds