9514 1404 393
Answer:
a) 320 m
b) 4.838 seconds, or 11.162 seconds
Step-by-step explanation:
a) S(8) = -5(8^2) +80(8) = -320 +640 = 320
The height 8 seconds after takeoff will be 320 meters.
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b) S(t) = 270
270 = -5t^2 +80t
-54 = t^2 -16t . . . . . . divide by -5
10 = t^2 -16t +64 . . . . add 64
±√10 = t -8 . . . . . . . . . . take the square root
t = 8 ±√10 ≈ {4.838, 11.162}
The rocket will be at a height of 270 meters at 4.838 and 11.162 seconds after takeoff.
