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## Homework Statement

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The path of a baseball relative to the ground can be modelled by the function

##d(t)=−t^2+8t+1##

, where d(t)represents the height of the ball in metres, and t represents time in seconds.

- What is the speed of the ball when it hits the ground?

## Homework Equations

## The Attempt at a Solution

##d(t)=-t^2+8t+1##

Using the quadratic to find the zeros, so I can find at what time the ball hits the ground.

##x=\frac {-b± \sqrt {b^2-4ac}} {2a}##

##x=\frac {-(8)± \sqrt {(8)^2-4(-1)(1)}} {2(-1)}##

x=-0.123 or x=8.123

Time can't be negative, therefore the ball htis the ground at 8.123 seconds.

I'm not sure how to find the velocity though. I thought I could take the first derivative of d(t)=−t2+8t+1 to find it but I couldn't figure it out that way. I think they want me to use limits somehow but I don't really know how.