The problem is: "A 0.00600-kg bullet traveling horizontally with a speed of 1.00*103 m/s enters an 19.2-kg door, imbedding itself 8.60 cm from the side opposite the hinges as in the figure below. The 1.00-m wide door is free to swing on its frictionless hinges. (a) Before it hits the door, does the bullet have angular momentum relative the door's axis of rotation? Yes? No? (b) If so, evaluate this angular momentum. (If not, enter zero.) (c) Is mechanical energy of the bullet-door system constant in this collision? Yes? No? (Answer without doing a calculation.) (d) At what angular speed does the door swing open immediately after the collision? (e) Calculate the energy of the bullet-door system and determine whether it is less than or equal to the kinetic energy of the bullet before the collision." I think I will be able to solve parts (d) and (e). For (a), the answer is yes, but I can't quite figure out why the answer is yes. For (c), the answer is no; but I am having trouble understanding how we can possibly know. Couldn't the kinetic energy of the bullet be completely absorbed as kinetic energy in the door? In this scenario, wouldn't mechanical energy be conserved?