Final answer:
The mechanical energy of a system is conserved when there is no external force doing work on the system and no energy is lost due to friction or other non-conservative forces. In this scenario, the mechanical energy is conserved, but the speed of the fish is less than the speed of the bird. The correct option is b) The mechanical energy is conserved, and the speed of the fish is less than 18.0 m/s.
Step-by-step explanation:
The mechanical energy of a system is conserved when there is no external force doing work on the system and no energy is lost due to friction or other non-conservative forces.
In this scenario, the bird dropping the fish is an internal force and does not affect the mechanical energy of the system. The initial mechanical energy of the system is equal to the kinetic energy of the bird, which is K = 0.5 * (mass of bird) * (speed of bird)^2. Once the fish is dropped, its potential energy is converted into kinetic energy as it falls. The final mechanical energy of the system is equal to the sum of the kinetic energy of the bird and the kinetic energy of the fish when it hits the water.
Therefore, the mechanical energy is conserved. However, the speed of the fish when it hits the water is less than the speed of the bird. This is because some of the initial potential energy of the fish is converted into kinetic energy as it falls, resulting in a decrease in the fish's speed.
Therefore, the correct option is b) The mechanical energy is conserved, and the speed of the fish is less than 18.0 m/s.