Question

A person on a bridge 175 feet above the ground drops his cell phone. The height of the falling cell phone is modeled by height = -16t^2 + 7t. How many seconds will it take the cell phone to reach 65 feet above the ground? (Round answer to 3 decimal places)

A) 1.352 seconds
B) 2.135 seconds
C) 3.221 seconds
D) 4.564 seconds

Answer 1

To find the number of seconds it will take the cell phone to reach 65 feet above the ground, we need to use the height equation -16t^2 + 7t = 65 and solve for t. After using the quadratic formula, the answer is approximately 1.352 seconds.

Step-by-step explanation:

To find the number of seconds it will take the cell phone to reach 65 feet above the ground, we need to set the height equation equal to 65 and solve for t.

-16t^2 + 7t = 65

Now we can solve this quadratic equation using factoring, completing the square, or the quadratic formula. Let's use the quadratic formula.

t = (-b ± √(b^2 - 4ac)) / (2a)

Plugging in the values from our equation (-16, 7, -65) into the quadratic formula and simplifying, we get t ≈ 1.352 seconds or t ≈ 3.221 seconds. Rounding to 3 decimal places, the answer is A) 1.352 seconds.