Quadratic function - word problem

May 2010
64
0
Palmy
Hi can any help shed some light on how i would go about completing this question (especially the graphing part)???

1) An object is thrown form a building and the height above the ground, y is given by the equation y=40 + 80t - 5t^2 where t is the time of flight(in seconds).

a) sketch a graph to represent the filght of the object?

b) What is the height after 4 seconds?

c) At what times is the height 120m?
 

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MHF Hall of Honor
Mar 2010
2,340
821
Chicago
Hi can any help shed some light on how i would go about completing this question (especially the graphing part)???

1) An object is thrown form a building and the height above the ground, y is given by the equation y=40 + 80t - 5t^2 where t is the time of flight(in seconds).

a) sketch a graph to represent the filght of the object?

b) What is the height after 4 seconds?

c) At what times is the height 120m?
This problem is more straightforward than it might appear at first.

a) Graph the given equation. Solve (algebraically or with a graphing calculator) the quadratic equation y = 0, to find that the object hits the ground at approximately t = 16.4853 seconds. The graph should thus be of the interval t in [0,16.4853]. It's a parabola.

b) Plug in t = 4 and find y.

c) Solve y = 120.