A ball on a carpet, while we pull it

[Cuzo]

Homework Statement

I have a problem. Imagine there is a ball on a carpet, I start to pull the carpet. The mass of the ball is 7 kilograms and the acceleration of the whole thing is 2m/s^2. What is the force with which I am pulling the carpet. Also what is the acceleration of the center of gravity (it is different as the ball is only rolling and not sliding on the carpet).
Thank you for answering.

http://www.shrani.si/f/3N/mM/4CG1g2q2/neimenovana.jpg

Homework Equations

F=ma²
Jar=Fr

The Attempt at a Solution

I came up with F=14 N and a=1,4ms² but am very unsure of the results.

 

[xboy]

Why should the the two accelerations different? Is the radius of the ball not supplied?