27) The angular momentum of a system remains constant A) all the time since it is a conserved quantity. B) when no torque acts on the system. C) when no net external force acts on the system. D) when the total kinetic energy is constant. E) when the linear momentum and the energy are constant. 28) While spinning down from 500.0 rpm to rest, a solid uniform flywheel (Disk) does 2.3 kJ of work. If the radius of the disk is 1.2 m, what is its mass? A) 3.0 kg B) 2.3 kg C) 2.6 kg D) 2.0 kg