A rock is thrown and follows the curve given by the equation d = -t2 + 4t + 5, where d is the distance in feet and t is the time
in seconds. When will the rock hit the ground? 9 seconds 5 seconds 2 seconds 1 second
1 answer:
Answer:
5 seconds
Step-by-step explanation:
The relationship between "d" and "the ground" is not described. If we assume that "d" is distance above the ground, then the rock will hit the ground when d=0. This gives rise to the quadratic equation ...
-t^2 +4t +5 = 0
-(t -5)(t +1) = 0
t = 5 or t = -1 are solutions. Only the positive solution is useful.
The rock will hit the ground after 5 seconds.
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