You have a figure that is combined with three figures. Two solid cylinders and one rectangle in the middle. Like this: OO
The two cylinders is rotating and are not sliding, so the whole figure moves to the right. The rectangle is connected with the two cylinders. Both cylinders and the rectangle has each mass M, so it will be three masses: M1=M2=M3. Also the two cylinders has the same radius: r1=r2
Proof that the kinetic energy equals to 2Mv2 (k=2Mv2)
I=1/2Mr2 (for solid cylinders)
The Attempt at a Solution
2*1/2*1/2Mv2(energy of 2 cylinders)+1/2Mv2(energy of rectangel)=1Mv2
I don't understand why it should be 2...