A firecracker shoots up from a hill 140 feet high with an initial speed of 100 feet per second. Using the formula H(t) = −16t2 + vt + s, approximately how long will it take the firecracker to hit the ground?

5 seconds

7 seconds

9 seconds

11 seconds

Question

A firecracker shoots up from a hill 140 feet high with an initial speed of 100 feet per second. Using the formula H(t) = −16t2 + vt + s, approximately how long will it take the firecracker to hit the ground?

 5 seconds

 7 seconds

 9 seconds

 11 seconds

anonymous · Answer

set s=140
    v=100

set the equation equals to 0

anonymous · Answer

let s = 140 as the fire cracker initial position is at 100 feet....
and v =  100 as the velocity is 100......if it has to reach the ground...the final height must be 0 so....make H(t)=0..
solve the quadratic equation....
dats approximately 9 seconds...

anonymous · Answer

im still lost.

anonymous · Answer

sry its approximately 7 sec..

anonymous · Answer

XD thanks. it was gonna take me all day.