Question

A firecracker shoots up from a hill 145 feet high, with an initial speed of 80 feet per second. Using the formula H(t) = −16t2 + vt + s, approximately how long will it take the firecracker to hit the ground?

13 seconds
11 seconds
Nine seconds
Six seconds

Answer 1

6 seconds

Explanation:

Answer 2

Plugging in the given values gives us:
0 = -16t^2 + 80t + 145
This a quadratic equation with two roots. Solving it using using the quadratic formula or by factoring, or by any other solution, the roots are:
6.4531 and -1.4131
We are dealing with time, so we choose the positive root.
Therefore, the answer is 6.4531 seconds