The height of a ball thrown upward from the ground is given by the quadratic function

h = 160t - 16
, where h is in feet and t is in seconds.

What is the reasonable domain for this function?
Responses
A {x: 0 ≤ x ≤ 10}{x: 0 ≤ x ≤ 10}
B {x: 0 ≤ x ≤ 160}{x: 0 ≤ x ≤ 160}
C {x: x ≥ 0}{x: x ≥ 0}
D all real numbers

1 answer

To determine the reasonable domain for the function \( h(t) = 160t - 16t^2 \), we need to consider the physical context of the problem. The function describes the height of a ball thrown upward, which implies that:

  1. Time \( t \) cannot be negative since we start measuring time from the moment the ball is thrown (which is at \( t = 0 \)).
  2. We also need to consider when the ball hits the ground (i.e., when \( h = 0 \)), which occurs at a certain positive time.

To find when the ball hits the ground, we set \( h(t) = 0 \):

\[ 160t - 16t^2 = 0 \] Factoring out \( t \):

\[ t(160 - 16t) = 0 \] This gives us two solutions:

  1. \( t = 0 \) (the starting time)
  2. \( 160 - 16t = 0 \) → \( 16t = 160 \) → \( t = 10 \)

Thus, the ball will be in the air from \( t = 0 \) to \( t = 10 \) seconds. Therefore, the reasonable domain of the function is the interval:

\[ 0 \leq t \leq 10 \]

This corresponds to option A: {x: 0 ≤ x ≤ 10}.