Speedy, the human fly, is shot from a cannon whose opening is 12 feet high. After 2 elapsed seconds, Speedy is 108 feet in the air. After 3 elapsed seconds, Speedy is again 108 feet in the air. Which of the following is the best representation of the quadratic function modeling Speedy’s height, h(t), as a function of elapsed time, t?

Respuesta :

The graph of Speedy's height in the air with time, which is based on a

quadratic function is a parabola.

  • The quadratic function modelling Speedy's height is given by the option; h(t) = -16·t² + 80·t + 12

Reasons:

The given parameters are;

The height of the cannon = 12 feet

Speedy's height after 2 seconds = 108 feet

Speedy's height after 3 seconds = 108 feet

Required: To select the best representation of the quadratic modelling Speedy's height, h(t), as a function of elapsed time, t?

Solution:

The path of Speedy's motion is a parabola

From the question, we have, that the initial height, at t = 0 is the height of the cannon = 12 feet

Therefore;

The equation has a constant term of 12

Given that the time it takes Speedy to rise above 108 feet and return to 108 feet = 3 - 2 = 1 second, we have;

The maximum height occurs between the 2nd and the 3rd second.

The path of a parabola is symmetric about the maximum point, therefore;

The maximum point occur at time [tex]\displaystyle 2 \, s + \frac{3 - 2}{2} \, s = 2.5 \, s[/tex]

Therefore, the x-coordinate of the vertex is t = 2.5 s

From the general equation of a parabola, a·x² + b·x + c, the x-coordinate of the vertex is; [tex]\displaystyle \mathbf{ -\frac{b}{2 \cdot a}}[/tex]

From the given option, we have the option; h(t) = -16·t² + 80·t + 12, which has;

Constant = 12

Vertex = [tex]\displaystyle -\frac{80}{2 \times (-16) } = 2.5[/tex]

Therefore;

The best representation of Speedy's height is; h(t) = -16·t² + 80·t + 12

The possible question options are;

h(t) = 1.07·t² + 5.33·t + 101.60

h(t) = 16·t² + 80·t + 12

h(t) = -1.07·t² + 5.33·t 101.60

h(t) = -16·t² + 80·t + 12

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