Answer: 3.98 s (approximately 4 s for practical purposes)
Explanation:
1) Equation given:
h(t) = - 4.9 t² + 18.9 t + 2.8
2) The time it will take the rocket fo hit the ground is given doing h (t) = 0
- 4.9 t² + 18.9 t + 2.8 = 0
3) You can solve that equation using the quadratic equation or working the equation to complete squares.
To use the quadratic equation you have a = - 4.9, b = 18.8, and c = 2.8
With that, t = [-18.8 +/- √ ( 18.8² - 4(-4.9)(2.8) ) ] / (2(-4.9) ) = 3.98 s
(I only picked the positive result because the negative does not have physical meaning).
