Question

Applying the Quadratic Formula

The height h (in feet) of an object t seconds after it is dropped can be modeled by the quadratic equation
h = -16t2 + h0, where h0 is the initial height of the object. Suppose a small rock dislodges from a ledge that is 255 ft above a canyon floor. Solve the equation h = -16t2 + 255 for t, using the quadratic formula to determine the time it takes the rock to reach the canyon floor.
A)t ≈ 0.87 s
B)t ≈ 4 s
C)t= 8.5 s
D)t = 16 s

Answer 1

B

Explanation:

edg 2020

Answer 2

B

Explanation:

The trick you need to employ is that when the rock hits the ground, the timer stops. So h must be taken as 0.

0 = - 16t^2 + 255 Set up the equation

- 255 = - 16t^2 Divide by -16

15.9375 = t^2 Switch

t^2 = 15.9375 Take the square root of both sides.

sqrt(t^2) = sqrt(15.9375)

t = 3.992 seconds

The closest answer is B