Question

A rock is dropped from a height of 100 feet. Calculate the time between when the rock was dropped and when it landed. If we choose "down" as positive and ignore air friction, the

function is h(t) = 16t^2 – 100.

A)t = 2.5 seconds

B)t = 6.25 seconds

C)t = 10 seconds

D)t = 12.5

Answer 1

A

Explanation:

the rock lands when it reaches height 0.

so, for what t is h(t) = 0 ?

16t² - 100 = 0

16t² = 100

now we pull the square root on both sides (we can ignore the negative solutions, as negative seconds don't make any sense in our scenario)

4t = 10

t = 10/4 = 5/2 = 2.5 seconds

so, A is correct.