Answer:
The arrow will take 4.19 seconds to hit the ground
The arrow will go 24 feet to reach its maximum height and it takes 2 seconds to reach this height
Step-by-step explanation:
The quadratic function is f(t) = -5t² + 20t + 4, where
f(t) is the height in feet
t is the time in seconds
If the arrow hit the ground that means h(t) = 0
→ Substitute h(t) by 0 and use the quadratic formula to find t
∵ h(t) = 0
∴ 0 = -5t² + 20t + 4
→ Switch the two sides
∴ -5t² + 20t + 4 = 0
→ Multiply all terms by -1 to make the coefficient of t² positive
∴ 5t² - 20t - 4 = 0
→ The quadratic formula is [tex]t=\frac{-b+-\sqrt{b^{2}-4ac}}{2a}[/tex] , where
- a is the coefficient of t²
- b is the coefficient of t
∵ a = 5, b = -20, c = -4
∴ [tex]t=\frac{-5+-\sqrt{(-20)^{2}-4(5)(-4)}}{2(5)}[/tex]
∴ [tex]t=\frac{-5+-\sqrt{400+80}}{10}[/tex]
→ Find the values of t in decimal
∴ t = 4.19 seconds OR t = -0.19 ⇒ refused because it is negative
∴ The arrow will take 4.19 seconds to hit the ground
The graph of this quadratic function is a parabola with maximum vertex (h, k), where
- h = [tex]\frac{-b}{2a}[/tex]
To find the maximum height and the time taking for this to occur find h and k where k is the maximum height and h is the time for this to occur
∵ f(t) = -5t² + 20t + 4
∵ a = -5 and b = 20
∴ h = [tex]-\frac{20}{2(-5)}=-\frac{20}{-10}=2[/tex]
∴ The time for the maximum height is 2 seconds
→ Now use it to find k
∵ k = f(h)
∴ k = f(2)
∵ f(2) = -5(2)²+ 20(2) + 4
∴ f(2) = -5(4) + 40 + 4
∴ f(2) = -20 + 40 + 4
∴ f(2) = 24
∴ k = 24
∴ The maximum height is 24 feet
The arrow will go 24 feet to reach its maximum height and it takes 2 seconds to reach this height
