Final answer:
In collision scenarios described, angular momentum is conserved due to no external torque acting on the system, while kinetic energy is not conserved because the collisions are inelastic. The conservation of linear momentum depends on external forces.
Step-by-step explanation:
The subject of this question is Physics, specifically under the topic of collisions and conservation laws in mechanics. In scenarios where a disk strikes and adheres to a stick that is nailed at one end to a frictionless surface, we examine the conservation principles that apply.
It is stated that angular momentum is conserved in both cases because, even though there is an unbalanced external force at the nail, this force does not exert any torque due to a lever arm of zero. However, kinetic energy is not conserved because the collisions are inelastic - the objects stick together instead of bouncing off each other. The conservation of linear momentum may not apply if the force at the nail has a component in the direction of the disk's initial velocity.
In another example involving a bullet and a disk, similarly, angular momentum would be conserved if no external torques act on the system. The question of whether momentum or kinetic energy is conserved depends on the specific details of the collision.