Make a graph
Your Y-axis is going to represent your height and the X-axis is going to represent time.
Now lets say that you are at the top of the Ferris wheel... your graph should have this shape:
http://www.wsd1.org/waec/math/Pre-Calculus%20Advanced/Trigonometry/Graphing/images/sinxbasic.gif
the top of that red line represents your height on top of the ferris wheel at time zero, the bottom of the valley of the red line represents the lowest part of the ride.
Hope that makes sense
:D