Question

An object is launched from a platform.

Answer 1

Answer:

  10

Step-by-step explanation:

Ground level is where h = 0, so solve the equation ...

  h(x) = 0

  -5(x -4)^2 +180 = 0 . . . . substitute for h(x)

  (x -4)^2 = 36 . . . . . . . . . . divide by -5, add 36

  x -4 = 6 . . . . . . . . . . . . . . positive square root*

  x = 10 . . . . . . add 4

The object will hit the ground 10 seconds after launch.

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* The negative square root also gives an answer that satisfies the equation, but is not in the practical domain. That answer would be x = -2. The equation is only useful for time at and after the launch time: x ≥ 0.