A uniform disc of mass $0.5 \mathrm{kg}$ and radius $r$ is projected with velocity $18 \mathrm{m} {\mathrm{s}}^{-1}$ at $t=0 \mathrm{s}$ on a rough horizontal surface. It starts off with a purely sliding motion at $t=0 \mathrm{s}$. After $2 \mathrm{s}$ it acquires a purely rolling motion (see figure). The total kinetic energy of the disc after $2 \mathrm{s}$ will be ______ $\mathrm{J}$.

(given, coefficient of friction is $0.3$ and $g=10 \mathrm{m} {\mathrm{s}}^{-2}$).

 

Hence, the correct answer is 54.