As shown in the figure, on a smooth horizontal plane, the bullet horizontally enters the wood block and remains in the wood block. Now, the bullet, spring and wood block are taken as the research object. In the whole process from the bullet's entry into the wood block to the shortest compression of the spring, the system () A. Conservation of energy, non conservation of mechanical energy B. non conservation of energy, non conservation of mechanical energy C. conservation of both energy and mechanical energy D. non conservation of energy, non conservation of mechanical energy

As shown in the figure, on a smooth horizontal plane, the bullet horizontally enters the wood block and remains in the wood block. Now, the bullet, spring and wood block are taken as the research object. In the whole process from the bullet's entry into the wood block to the shortest compression of the spring, the system () A. Conservation of energy, non conservation of mechanical energy B. non conservation of energy, non conservation of mechanical energy C. conservation of both energy and mechanical energy D. non conservation of energy, non conservation of mechanical energy

In the whole process of the system from the beginning of the bullet to the compression of the spring to the shortest time, the sum of the external forces on the system is not zero because of the strong effect of the wall on the spring, so the momentum of the system is not conserved. In the whole process, because the internal energy is generated in the process of the bullet into the wood block, the mechanical energy of the system is not conserved. But the energy is conserved. So a is correct, B, C and D are wrong So choose a