A firecracker shoots up from a hill 160 feet high, with an initial speed of 90 feet per second. Using the formula H(t) = -16t2 + vt + s, approximately how long will it take the firecracker to hit the ground?

Five seconds

Six seconds

Seven seconds

Eight seconds

Question

A firecracker shoots up from a hill 160 feet high, with an initial speed of 90 feet per second. Using the formula H(t) = -16t2 + vt + s, approximately how long will it take the firecracker to hit the ground? 

 Five seconds

 Six seconds

 Seven seconds

 Eight seconds

anonymous · Answer

@phi @undeadknight26 please help!

bloomlocke367 · Answer

I'm assuming that v=velocity (speed) and t=time?

anonymous · Answer

Yeah

bloomlocke367 · Answer

and what about s?

anonymous · Answer

I got about six

anonymous · Answer

the starting height

freckles · Answer

when the object is on the ground the height is 0 at that time

freckles · Answer

so just solve H(x)=0 for x

freckles · Answer

and yes x is suppose to be t

anonymous · Answer

??? But don't you have to find the line of symmetry...? And then multiple that by two

anonymous · Answer

multiply*

anonymous · Answer

so 90/32 = 2.8125 is the line of symmetry

freckles · Answer

yep you will need to use the vertex of the parabola as the initial time place

anonymous · Answer

but you don't have to find the vertex because we don't have to know the height

anonymous · Answer

wait... but there's a y-intercept of 160 so no I would have to find the zeroes instead

freckles · Answer

you know what no I change my mind 
the vertex of the parabola isn't the intial

freckles · Answer

the firecracker still goes up before going down from there

freckles · Answer

so yep you are just suppose to solve H(t)=0 for t

anonymous · Answer

Okay I got it I think I can do the rest on my own. Thanks :)

freckles · Answer

k