Question

A professor uses a video camera to record the motion of an object falling from a height of 250 meters. The function f(x) = –5x2 + 250 can be used to represent the approximate height of the object off the ground after x seconds. Which is the best estimate for the amount of time elapsed when the object is 120 meters off the ground?

4 seconds
5 seconds
6 seconds
7 seconds

Answer 1

Set f(x) = 120:

-5x^2 + 250 = 120
-5x^2 = -130
x^2 = 26
x = sqrt(26) ≈ 5.10

So the best estimate is 5 seconds.