Two discs, each having moment of inertia 5 kg m2 about its central axis, rotating with speeds 10 rad s-1 and 20 rad s-1 are brought in contact face to face with their axesof rotation coincided. The loss of kinetic energy in the process is

When brought in contact , due to kinetic friction , both acquire common velocities.Applying conservation of angular momentum,(5+5)ω'=5×10+5×20=150⇒ω'=15rads−1Initial kinetic energy=12×5×10×10+12×5×20×20=250+1000=1250JFinal kinetic energy =12×10×15×15=1125JLoss of kinetic energy =(1250−1125)J=125J