what is the quadratic equation?

Question

An object is launched from 9 feet above ground level directly upward with an initial velocity of 30 feet per second. The gravitational pull of the Earth is about 16 feet per second squared. Which quadratic equation in standard form correctly models this situation in order to determine after how many seconds, t, the object will be 4 feet above the ground?

Answer 1

y = -16t² + 30t + 9 therefore 

 

4 = -16t² + 30t + 9

Answer 2

h(t) = -gt²/2 + v₀t+ h₀

 

g = 32 ft/s²

v₀ = 30 ft/s

h₀ = 9 ft

 

h(t) = -16t² + 30t + 9

 

Whet h = 4,

 

4 = -16t² + 30t + 9

 

In standard form,

 

-16t² + 30t + 5 = 0

 

Now solve for t using the quadratic formula.  You will get a positive and a negative solution.  Since time starts at t = 0, discard the negative solution.