Question

HELP!!!!!!!

A falling object travels a distance given by the formula d=3t+5t2, where d is measured in feet and t is measured in seconds. How many seconds will it take for the object to travel 84 feet?

Answer 1

Approximately 3.81 seconds

Explanation:

d = 3t + 5t²

d = 84

84 = 3t + 5t²

3t + 5t² - 84 = 0

5t² + 3t - 84 = 0

5(t² + 3/5t - 84/5) = 0

5(((t + 3/10)² - 9/100) - 84/5) = 0

5((t + 3/10)² - 9/100 - 84/5) = 0

5((t + 3/10)² - 9/100 - 1680/100) = 0

5((t + 3/10)² - 1689/100) = 0

5(t + 3/10)² - 1689/20 = 0

5(t + 3/10)² = 1689/20

(t + 3/10)² = 1689/100

t + 3/10 = ±√(1689)/10

t = -3/10 ± √(1689)/10

t = -3/10 ± ≈41.1/10

t = -3/10 ± ≈4.11

t ≈ -0.3 ± 4.11

t [can only be positive] ≈ 4.11 - 0.3

t ≈ 3.81