Question

A firecracker shoots up from a hill 165 feet high with an initial speed of 110 feet per second. Using the formula H(t) = −16t2 + vt + s, determine how long it will take the firecracker to hit the ground.

7.2 seconds

7.5 seconds

7.8 seconds

8.1 seconds

Answer 1

You have an initial condition where H(0) = 165. This will help you solve for s. You also know that the initial velocity (v) = 110ft/s. You just need to solve for the final time (lets call it f) when H(f) = 0.

Answer 2

H(0) = -16(0)^2 + 110(0) + s = 165 Can you see what s must be?
H(f) = -16(f)^2 + 110(f) + s = 0

Answer 3

I am assuming the firecracker lands somewhere 165 feet below the place it was fired from.

Answer 4

I'm getting it so far.

Answer 5

Wait so whats the answer?

Answer 6

8.1 D

Answer 7

Thank you!