Question

A rock is dropped from a bridge 320 feet above a river. The pathway that the rock takes can be modeled by the equation h=-16t squared+320. How long will it take the rock to reach the river?

A. 2.5 sec
B. 3.5 sec
C. 3.8 sec
D. 4.5 sec

Answer 1

D. 4.5 sec

Explanation:

Once the rock is on the ground it has no height (h=0)

h = -16t² + 320

0 = -16t² + 320

16t² = 320

t² = 20

t² = 20

t = √20

t= √4x5

t = 2√5

around 4.5 seconds