Answer:
a) The car was moving at a speed of 
b) The negative sign of 
denotes that the observer is coming towards the police car which is the source of the sound.
c) 
Explanation:
Given:
- original frequency of the source,
- speed of the source,
- velocity of the obstacle car be,
- speed of sound,
- observed frequency,
<u>Using the equation from the Doppler's effect:</u>
a)
The car was moving at a speed of
b)
The negative sign of denotes that the observer is coming towards the police car which is the source of the sound.
c)
Now when, 
Then, 
Using the Doppler's eq.:
Answer:
shown in the attachment
Explanation:
The detailed step by step and necessary mathematical application is as shown in the attachment.
Answer:
at T = 0ºC the change of state is from the solid state to the gaseous state
Explanation:
In this exercise we are asked about the changes of state, from the data we will assume that the material is water.
Water can exist in three solid states, liquid and gas, in a graph of pressure ℗ against temperature (T) there is a point called triple at T = 0.01ºC, below this point the curve has two states at high pressure solid and low pressure gas.
As a result of the previous ones at T = 0ºC the change of state is from the solid state to the gaseous state
The correct answer in this case is B. Harmonic.
The remaining answers refer to other parts of a musical composition, and some such as the pitch can even be found in the study of human voice.
The vanishing of an ionic solid (like table salt) would be an example of acting like a solvent
