A firecracker shoots up from a hill 145 feet high, with an initial speed of 80 feet per second. Using the formula H(t) = -16t^2 + vt + s, approximately how long will it take the firecracker to hit the ground?

13 seconds

11 seconds

Nine seconds

Six seconds

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) = -16t^2 + vt + s, approximately how long will it take the firecracker to hit the ground? 

 13 seconds

 11 seconds

 Nine seconds

 Six seconds

kirbykirby · Answer

$s$ is your position, so $s=145$
$v$ is your velocity, which would be $80$

so $H(t)=-16t^2+80t+145$

The firecracker will hit the ground when the height $H(t)$ reaches 0, i.e. solve $$ 0=-16t^2+80t+145$$, which will solve  for the time $t$

bigbosssaint21 · Answer

im not really sure

kirbykirby · Answer

this is a quadratic equation, you can use the quadratic formula to find $t$