Question

[9.06] 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?

A 13
B 11
C 9
D 6

Answer 1

Please help! MEDAL AND FAN for best answer!

Answer 2

@jakejoker please help!

Answer 3

what formula is that?

Answer 4

It is one of the Algebra formulas @jakejoker

Answer 5

The function will be: y = -16t^2 + 80t + 145
I could explain where the equation came from, but that'll take too much time.

From here, you use the quadratic formula to solve for when y = 0. Most likely you will get a positive and a negative answer, so you will choose the positive one only. You cannot have negative time.

Answer 6

Wait so the answer is 6? @IAmSinged

Answer 7

@IAmSinged are the formula the same for different unit (I use SI unit)

Answer 8

OHHH i see. @IAmSinged Thank you.

Answer 9

The equation is in ft. The formula is the same because of the calculus behind it.

Answer 10

but the gravity acceleration in SI unit is approx 9.8...wouldn't that make the different?

Answer 11

or they have g value in ft?

Answer 12

It doesn't matter if you're using meters, ft, inches, etc. The formula will always be:
-(gravity in whatever units)t^2 + (velocity in the same unit basis)t + height in the same unit basis

Answer 13

Ok thank you @IAmSinged