Consider a disc of mass 5kg , radius 2m , rotating with angular...

Initial angular momentum, ${L}_{i} = I{\omega}_{i} = \dfrac{M{R}^{2}}{2} \cdot \omega = 100kg{m}^{2}{s}^{- 1}$

Initial kinetic energy, ${E}_{i} = \dfrac{1}{2} \cdot \dfrac{M{R}^{2}}{2} \cdot {\omega}^{2} = 500J$

From conservation of angular momentum, we can write

$\overset{\to}{L}i = \overset{\to}{L}f ⇒ 100 = 2I{\omega}_{f}$

$⇒ {\omega}_{f} = 5rad{s}^{- 1}$

${E}_{f} = 2 \times \dfrac{1}{2} \cdot \dfrac{5 ( 2{)}^{2}}{2} \cdot ( 5{)}^{2} = 250J$

Therefore, required energy loss $\DeltaE = 250J$