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

A boy stands over the centre of a horizontal platform which is rotating freely with a speed of 2 revolutions/s about a vertical axis through the centre of the platform and straight up through the boy. He holds 2 kg masses in each of his hands close to his body. The. combined moment of inertia of the system is 1 kg$\times$metre². The boy now stretches his arms so as to hold the masses far from his body. In this situation, the moment of inertia of the system increases to 2kg$\times$metre². The kinetic energy of the system in the latter case as compared with that in the previous case will