Here we go. My abbreviations; KE = Kinetic Energy; GPE = Gravitational Potential Energy.
So first off, we know the fish has KE right when the bird releases it. Why? Because it has horizontal velocity after released! So let’s calculate it: KE = 1/2(m)(V)^2 KE = 1/2(2)(18)^2 KE = 324 J
Nice! We also know that the fish has GPE at its maximum height before release: GPE = mgh GPE = (2)(9.81)(5.40) GPE = 105.95 J
Now, based on the *queue dramatic voice* LAW OF CONSERVATION OF ENERGY, we know all of the initial energy of the fish will be equal to the amount of final energy. And since the only form of energy when it hits the water is KE, we can write: KEi + GPEi = KEf (Remember - we found the initial energies before!) (324) + (105.95) = KEf KEf = 429.95J And that’s you’re final answer! Notice how this value is MORE than the initial KE from before (324 J) - this is because all of the initial GPE from before was transformed into more KE as the fish fell (h decreased) and sped up (V increased).
Is there any numbers to your question? Keep in mind, the energy is conserved in a pendulum. Here’s more information: https://blogs.bu.edu/ggarber/interlace/pendulum/energy-in-a-pendulum/
