Question

A model rocket was launched from the top of a building. The rocket's approximate height can be modeled by the quadratic equation h = -4.9t2 + 53.9t + 127.4, where h is the rocket's height, in meters, after t seconds. When factored, this equation is h = -4.9(t - 13)(t + 2). What is a reasonable time for it to take the rocket to land on the ground?

Answer 1

You are looking for the x-intercepts. Only one intercept will be valid because time must be positive!

0 = -4.9(t - 13)(t + 2)

0 = -4.9 , 0 = t - 13 , 0 = t + 2

False, t = 13 t = -2 (not valid)

Answer: 13 seconds