Explanation:
Given that,
Frequency of train horn, f = 218 Hz
Speed of train, 
The speed of sound, V = 344 m/s (say)
The speed of the observed person, 
(a) When the train approaches you, the Doppler's effect gives the frequency as follows :

(b) When the train moves away from you, the Doppler's effect gives the frequency as follows :

Hence, this is the required solution.
Answer:
Runner A
Explanation:
Both B and C finished the race from 25 seconds
But A runner finished it from 20 seconds
Frequency = how many waves you get per sec
Period = how long each wave takes
Period = 1/frequency
Explanation:
Most waves appear complex because they result from two or more simple waves that combine as they come together at the same place at the same time—a phenomenon called superposition. Waves superimpose by adding their disturbances; each disturbance corresponds to a force, and all the forces add
introurself please
Answer:
It is an example of negative feedback mechanism
Explanation:
Negative feedback mechanism is the process by which the output of a system, process or mechanism is fed back into the input in order to reduce the error in the system.
In the system described in this question, the reabsorption of water is the output, a feedback signal is sent to the control center, which is the input in order to control the release of the hormone responsible for reabsorption of water into the blood.