Two identical discs having radius R are rotating in opposite sense are joined with light rod having frictionless groove A and B and placed on rough horizontal surface as shown in figure. Initially translation velocity of each disc is zero. Then:

 
 
 Angular momentum conservation gives
 $$\begin{gathered} \left(2{\omega }_0\right)\frac{m{R}^2}{2}-\frac{m{R}^2}{2}\left({\omega }_0\right)=2m{v}_{C}R+\frac{2m{R}^2}{2}\omega \text{'} \\ \frac{m{R}^2}{2}{\omega }_0=2m{v}_{C}R+mR{v}_C (Since{v}_C=\omega \text{'}R) \\ {v}_C=\frac{R{\omega }_0}{6} \end{gathered}$$
* Second figure shows that rod is under stress & hence its length will increase.
* Finally when the discs roll purely, there is no friction & hence to tensile stress 
* Since friction is kinetic therefore mechanical energy will decrease.