Physics Rotational Disk Question?

Posted on 2016-11-17 18:43:00 in Physics by CHENGHAO

A homogeneous disk of 5 cm radius and 10 kg 
mass rotates on an axle AB of length 0.5 m and rotates 
about a fixed point A. The disk is constrained to roll on a 
horizontal floor. Given an angular velocity of 30 rad/s in the 
x direction and -3 rad/s in the y direction, the kinetic energy 
of the disk is 
A. 5.6J 
B. 17J 
C. 23J 
D. 34J 

Here is my solution: 
1/2 x 10kg x (0.05m x 30 rad/s)^2+1/2 x [10kg x (-3 rad/s)]^2 = 22.5J which is C 

However on the solution it says 
1/2 x 1/2 x 10kg x (0.05m x 30 rad/s)^2+1/2 x [10kg x (-3 rad/s)]^2 = 16.9J which is B 

Can anyone tell me why there is extra 1/2 in front? Thank you.

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