Ferris wheel magnitude and period

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Homework Statement

A woman rides a carnival Ferris wheel at radius 21 m, completing 4.2 turns about its horizontal axis every minute. What are (a) the period of the motion, and the magnitude of her centripetal acceleration at (b) the highest point and (c) the lowest point?

Homework Equations

The Attempt at a Solution

How should I go about solving this one? Also are there any sites that can explain 2d and 3d motion better? My book is a little lacking.

 

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So I have t= 14.285 but I really am unsure of how to find the max/min.