standard_description: Recognize that sequences are functions, sometimes defined recursively, whose domain is a subset of the integers. For example, the Fibonacci sequence is defined recursively by f(0) = f(1) = 1, f(n+1) = f(n) + f(n-1) for n ³ 1.
problem_activity: Task
A wheel of radius 0.2 meters begins to move along a flat surface so that the center of the wheel moves forward at a constant speed of 2.4 meters per second.  At the moment the wheel begins to turn, a marked point $P$ on the wheel is touching the flat surface.
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Write an algebraic expression for the function $y$ that gives the height (in meters) of the point $P$, measured from the flat surface, as a function of $t$, the number of seconds after the wheel begins moving.
Sketch a graph of the function $y$ for $t>0$.  What do you notice about the graph?  Explain your observations in terms of the real-world context given in this problem.
We define the horizontal position of the point $P$ to be the number of meters the point has traveled forward from its starting position, disregarding any vertical movement the point has made.  Write an algebraic expression for the function $x$ that gives the horizontal position (in meters) of the point $P$ as a function of $t$, the number of seconds after the wheel begins moving.
Sketch a graph of the function $x$ for $t>0.$  Is there a time when the point $P$ is moving backwards?  Use your graph to justify your answer.


aligns: no