Question

A gust of wind forces a rock to fall off a cliff that's 20 feet high. This is represented by the function h(t) = –16t2 + 20, where t represents the time measured in seconds, and h represents height above the ground. Approximate how many seconds it takes for the rock to hit the ground.

Answer Options:

A.) 1.25 seconds

B.) 1.5 seconds

C.) 1.12 seconds

D.) 1 second

Answer 1

Answer: C. 1.12 seconds

Step-by-step explanation: The rock hits the ground when h(t) = 0, or at the x-intercept of the graphed function. Input the function into a graphing calculator, and use the intersection button to determine when the graph hits the ground at y = 0. The time it takes for the rock to hit the ground is 1.12 seconds.

Answer 2

Answer: C.) 1.12 seconds

Explanation:

Hi, to answer this question we have to substitute h=0 (when the rock hits the ground the height above it is 0) in the equation given:

h (t) = –16t2 + 20

Solving for t (time)

0= –16t2 + 20

16t2=20

t2=20/16

t=√1.25 =1.12 seconds (option C)

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