19. If you are watching a moving train, what would happen to the pitch of the whistle at a crossing as the locomotive approaches and then passes by the crossing?
a. The pitch would remain the same.
b. The pitch would increase suddenly as the train passed.
C. The pitch would decrease and then increase again.
d. The pitch would decrease suddenly as the train passed.

chemical energy --> gravitational potential energy --> kinetic energy --> elastic potential energy --> gravitational potential energy

explanation:

when emma starts the hike, the chemical energy stored in her body is used to climb up the mountain, and so she gains gravitational potential energy (because at the end, she will be at a higher height h above the ground). then she goes bungee jumping: as she falls, this gravitational potential energy is converted into kinetic energy (because her speed increases as she falls down), until the point when the rope stretches, and she stops moving. at that moment, all the kinetic energy is converted into elastic potential energy due to the stretching of the rope. then, this energy is released because the rope returns to its natural length, and emma gains a small increase in altitude , so she gains some gravitational potential energy.