A uniform disc of mass 0 . 5kg and radius r is projected with...

Acceleration of the disc, $a = - {\mu}_{k}g = - 3m{s}^{- 2}$.

Now, velocity of the centre of mass

$v = u + at = 18 - 3 \times 2$

$⇒ v = 12m{s}^{- 1}$

Now total kinetic energy during pure rolling($v = \omegar$) will become,

$KE = \dfrac{1}{2}m{v}^{2} + \dfrac{1}{2}I{\omega}^{2} = \dfrac{1}{2}m{v}^{2} + \dfrac{1}{2}\dfrac{m{r}^{2}}{2}\dfrac{{v}^{2}}{{r}^{2}}$

$⇒ KE = \dfrac{3}{4}m{v}^{2}$

$= 3 \times 18 = 54J$