4. A train passes a stationary observer. Which of the following best describes how the amplitude and the apparent frequency of the sound waves heard by the observer change as the train
moves away?
A. Both the amplitude and the apparent frequency increase.
B. Both the amplitude and apparent frequency decrease.
C. The amplitude of the sound waves increases, and the apparent frequency decreases.
D. The amplitude of the sound waves decreases, and the apparent frequency increases.

think its the third option

u

explanation:

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.