<h2>We know that</h2>
The initial height is 20 feet above the ground.
The function to model the velocity is

Where <em>s</em> represents the distance in feet.
Mathematically, this function has all real numbers as a domain. However, that will no make sense for this situation, because it would use negative numbers for the distance <em>s</em> which does not make sense.
Therefore, the domain, in this case, would be all real numbers greater than or equal to zero, but less than or equal to 20.
<em>The reason for this domain is that the ball will go from 20 feet above the ground to zero feet on the ground.</em>
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Using interval notation would be