A football is kicked into the air from an initial height of 4 feet. The height, in feet, of the football above the ground is given by s (t)=-16^2+50t+4, where t is time, in seconds, and t>=0. At what time will the football be 25 feet above the ground?
3.625 seconds
3.20 seconds
0.5 seconds or 3.625 seconds
0.5 seconds or 2.625 seconds



2 years ago Comment

To answer the question above, substitute the given value of height. 
                                          25 = -16x²  + 50t + 4
Solving the following equation by the use of quadratic formula,
                             x = (-b +/- sqrt (b² - 4ac)) / 2a
Subsituting the known values of a, b, and c
                             x = (-50 +/- sqrt (50² - 4(-16)(-21)) / 2x-16
The values of x are 0.5 and 2.625. Therefore, the answer is the fourth choice.