A uniform disc of mass 0.5 kg and radius r is projected with velocity 18 m / s at t =0 s on a rough horizontal surface. It starts off with a purely…

A uniform disc of mass $\displaystyle 0.5$ kg and radius $\displaystyle r$ is projected with velocity $\displaystyle 18 \mathrm{~m} / \mathrm{s}$ at $\displaystyle \mathrm{t}=0 \mathrm{~s}$ on a rough horizontal surface. It starts off with a purely sliding motion at $\displaystyle \mathrm{t}=0 \mathrm{~s}$. After 2s it acquires a purely rolling motion (see figure). The total kinetic energy of the disc after $\displaystyle 2$ s will be $\displaystyle \_\_\_\_$ J (given, coefficient of friction is $\displaystyle 0.3$ and $\displaystyle \mathrm{g}=10 \mathrm{~m} / \mathrm{s}^2$ ).