Circular Momentum Homework: Find Radius of a Particle in Counterclockwise Motion

[TS656577]

Homework Statement

At t1 = 1 s, the acceleration of a particle moving at constant speed in counterclockwise circular motion is http://edugen.wiley.com/edugen/shared/assignment/test/session.quest365780entrance1_N10039.mml?size=14&algorithm=1&rnd=1201725654088
At t2 = 3 s (less than one period later), the acceleration is http://edugen.wiley.com/edugen/shared/assignment/test/session.quest365780entrance1_N10080.mml?size=14&algorithm=1&rnd=1201726050259
The period is more than 2 s. What is the radius of the circle?

Homework Equations

a=v^2/r

The Attempt at a Solution

I figured out the period is 2.67 seconds and the acceleration is 7.21 m/s^2. Then I get stuck

 

[TS656577]

Also, if those links don't work, reply and ill try my best to fix them