When exactly are they conserved? For example, one question involved a person jumping off of a circular platform (that rotated without friction), and when the student jumped off tangentially, the platform started spinning. The question asked which of the following is conserved - angular momentum, linear momentum, and kinetic energy - and only angular momentum ended up being the correct answer. It is clear that linear momentum wouldn't be conserved using the linear speed of the entire platform, but if the instantaneous linear speed of the point on the platform where the student jumped off were used as the speed of the platform, then would linear momentum be conserved? And kinetic energy wasn't conserved because the person and the platform were stuck together, kind of like an inelastic collision? I know that linear momentum is conserved in a system without any external forces, and angular momentum is conserved in a system without any external torques, but I'm still not completely sure for situations like the one I mentioned, and when angular momentum and linear momentum are combined in general.