A firecracker shoots up from a hill 145 feet high, with an initial speed of 80 feet per second. Using the formula H(t) = -16t2 + 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) = -16t2 + vt + s, approximately how long will it take the firecracker to hit the ground? 

 13 seconds

 11 seconds

 Nine seconds 


Six seconds

jim_thompson5910 · Answer

v = 80 is the initial speed
s = 145 is the initial height

jim_thompson5910 · Answer

solve for t (use the quadratic formula)

H(t) = -16t^2 + 80t + 145

0 = -16t^2 + 80t + 145

-16t^2 + 80t + 145 = 0

In this case, a = -16, b = 80, c = 145