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?

Question

anonymous · Answer

ok i will use calculus based approach
are you familiar with derivatives?

anonymous · Answer

not really

anonymous · Answer

i think it is from the calculus course
isn't it?

anonymous · Answer

im only in algebra 1

anonymous · Answer

anyway
taking derivative of H(t)
$$H'(t)=-16*2(t)+v=-32t+v$$

anonymous · Answer

are u okay with this ?

anonymous · Answer

yeah

anonymous · Answer

ok
set it equal to zero
$$-32t+v=0$$
solve for t
$$32t=v$$
$$t=\frac{v}{32}$$
but 
v=100 
$$t=\frac{100}{32}=3.125 $$

anonymous · Answer

put t=3.125 in the original equation
let e know what you got?

anonymous · Answer

okay hold on

anonymous · Answer

do not forget to use s=0 and v=100 along with t=3.125 in the equation !

anonymous · Answer

i dont think i did it right? but i got h(t)=156...

anonymous · Answer

you got it correct!