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?

Medal and Fan!! Help please...

Answer 1

well after substituting you get

\[H(t) = -16t^2 + 90t + 160\]

to find the time when it hits the ground set H(t) = 0

and then solve for t. Only consider the positive time value.

I think you need to general quadratic formula.

Answer 2

I got 8 but some how i feel thats wrong can u walk me through the equation?

Answer 3

well you can divide very term by 2

\[0 = -8t^2 + 45t + 80\]


then

\[t = \frac{-45 \pm \sqrt{45^2 - 4 \times -8 \times 80}}{2 \times -8}\]

\[t = \frac{-45 \pm \sqrt{4585}}{-32}\]

hope that helps

Answer 4

so it is 8...

Answer 5

oops should be

\[t = \frac{45 + \sqrt{4585}}{16}\]

the denominator should be -16 not -32

and I didn't get 8

Answer 6

ok I just re did it and I got 6 ... please tell me im right...@campbell_st

Answer 7

well \[\sqrt{4585} = 67.7\]

so solve

\[t = \frac{45 + 67.7}{16}\]

Answer 8

thanks for the help I got it ^.^