Question

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?

A: Five seconds
B: Seven seconds
C: Nine seconds
D: 11 seconds

Answer 1

Answer: it’s b, 7 seconds. Just took the test

Explanation:

Answer 2

H(t) = −16t^2 + vt + s


H(t) = −16t^2 + 100t + 140

H(t) = 0 = −16t^2 + 100t + 140

16t^2 - 100t -140 = 0

t = [100 +/- √ (100^2 -4(16)(-140) ) ] /(2(16))

t = 7.43 and t = - 1.18.

El que tiene sentido para la pregunta es t = 7.43 s.

Option B) 7 s (approximately)